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Accounts Receivable, Net (Tables)

12 Months Ended

Dec. 31, 2019

December 31
(in millions)	2019			2018
Customer receivables	$	564.4		$	514.1
Other current receivables		14.0			12.5
		578.4			526.6
Less: Allowances		(4.7	)		(3.3	)
Total	$	573.7		$	523.3

Consolidated Statements of Earnings - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total revenues	$ 4,739.1	$ 4,244.3	$ 3,965.6
Total cost of revenues	3,560.1	3,277.7	2,993.7
Gross Profit	1,179.0	966.6	971.9
Selling, general and administrative expenses	302.7	280.6	262.1
Acquisition-related expenses, net	0.5	13.5	8.6
Other operating (income) and expenses, net	(9.1)	(18.2)	0.8
Earnings from Operations	884.9	690.7	700.4
Interest expense	129.3	137.1	91.5
Other nonoperating expenses and (income), net	7.3	(22.5)	(10.0)
Earnings before income tax expense (benefit)	748.3	576.1	618.9
Income tax expense (benefit)	136.3	105.7	(94.5)
Consolidated net earnings	612.0	470.4	713.4
Less: Net earnings attributable to noncontrolling interests	0.1	0.4	0.1
Net Earnings Attributable to Martin Marietta	$ 611.9	$ 470.0	$ 713.3
Net Earnings Attributable to Martin Marietta Per Common Share (see Note A)
Basic attributable to common shareholders	$ 9.77	$ 7.46	$ 11.30
Diluted attributable to common shareholders	$ 9.74	$ 7.43	$ 11.25
Weighted-Average Common Shares Outstanding
Basic	62.5	62.9	62.9
Diluted	62.7	63.1	63.2
Products and Services
Total revenues	$ 4,422.3	$ 3,980.4	$ 3,723.5
Total cost of revenues	3,239.1	3,009.8	2,749.5
Freight
Total revenues	316.8	263.9	242.1
Total cost of revenues	$ 321.0	$ 267.9	$ 244.2

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 21.0	$ 44.9
Accounts receivable, net	573.7	523.3
Inventories, net	690.8	663.0
Other current assets	141.2	134.6
Total Current Assets	1,426.7	1,365.8
Property, plant and equipment, net	5,206.0	5,157.2
Goodwill	2,396.8	2,399.1
Other intangibles, net	486.8	501.3
Operating lease right-of-use assets, net	481.9
Other noncurrent assets	133.4	128.0
Total Assets	10,131.6	9,551.4
Current Liabilities:
Accounts payable	229.6	210.8
Accrued salaries, benefits and payroll taxes	56.7	51.4
Accrued insurance and other taxes	63.1	63.6
Current maturities of long-term debt	340.0	390.0
Operating lease liabilities	52.7
Other current liabilities	96.4	70.9
Total Current Liabilities	838.5	786.7
Long-term debt	2,433.6	2,730.4
Deferred income taxes, net	733.0	705.6
Noncurrent operating lease liabilities	433.9
Other noncurrent liabilities	339.3	379.3
Total Liabilities	4,778.3	4,602.0
Equity:
Common stock ($0.01 par value; 100.0 shares authorized; 62.4 and 62.5 shares outstanding at December 31, 2019 and 2018, respectively)	0.6	0.6
Preferred stock ($0.01 par value; 10.0 shares authorized; no shares outstanding)
Additional paid-in capital	3,418.8	3,396.1
Accumulated other comprehensive loss	(145.8)	(143.6)
Retained earnings	2,077.2	1,693.3
Total Shareholders’ Equity	5,350.8	4,946.4
Noncontrolling interests	2.5	3.0
Total Equity	5,353.3	4,949.4
Total Liabilities and Equity	$ 10,131.6	$ 9,551.4

Accounting Policies - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net earnings attributable to Martin Marietta	$ 611.9	$ 470.0	$ 713.3
Less: Distributed and undistributed earnings attributable to unvested participating securities	0.9	0.8	2.0
Basic and diluted net earnings attributable to common shareholders attributable to Martin Marietta	$ 611.0	$ 469.2	$ 711.3
Basic weighted-average common shares outstanding	62.5	62.9	62.9
Effect of dilutive employee and director awards	0.2	0.2	0.3
Diluted weighted-average common shares outstanding	62.7	63.1	63.2

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Long-Term Debt - Schedule of Principal Amount, Effective Interest Rate and Maturity Date for Corporation's Senior Notes (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Principal Amount	$ 400,000,000.0
Effective Interest Rate	4.25%
Maturity Date	Jul. 02, 2024
7% Debentures, Due 2025
Debt Instrument [Line Items]
Principal Amount	$ 125,000,000.0
Effective Interest Rate	7.12%
Maturity Date	Dec. 01, 2025
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Principal Amount	$ 300,000,000.0
Effective Interest Rate	3.47%
Maturity Date	Jun. 01, 2027
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Principal Amount	$ 500,000,000.0
Effective Interest Rate	3.53%
Maturity Date	Dec. 15, 2027
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Principal Amount	$ 230,000,000.0
Effective Interest Rate	6.45%
Maturity Date	May 01, 2037
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Principal Amount	$ 600,000,000.0
Effective Interest Rate	4.27%
Maturity Date	Dec. 15, 2047
Floating Rate Senior Notes, Due 2020
Debt Instrument [Line Items]
Principal Amount	$ 300,000,000.0
Effective Interest Rate	2.55%	3.30%
Debt Instrument Effective Interest Rate	Three-month LIBOR + 0.65%
Maturity Date	May 22, 2020

Consolidated Statements of Total Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss) Earnings	Retained Earnings	Total Shareholders’ Equity	Noncontrolling Interests
Beginning Balance at Dec. 31, 2016	$ 4,142.6	$ 0.6	$ 3,334.5	$ (130.7)	$ 935.7	$ 4,140.1	$ 2.5
Beginning Balance (in shares) at Dec. 31, 2016		63,200,000
Consolidated net earnings	713.4				713.3	713.3	0.1
Other comprehensive (loss) earnings	1.6			1.6		1.6
Dividends declared	(108.9)				(108.9)	(108.9)
Issuances of common stock for stock award plans	14.9		14.9			14.9
Issuances of common stock for stock award plans (in shares)		200,000
Shares withheld for employees’ income tax obligations	(11.8)		(11.8)			(11.8)
Repurchases of common stock	$ (100.0)				(100.0)	(100.0)
Repurchases of common stock, Shares	(500,000)	(500,000)
Stock-based compensation expense	$ 30.5		30.5			30.5
Contribution from owners of noncontrolling interest	0.2						0.2
Ending Balance at Dec. 31, 2017	4,682.5	$ 0.6	3,368.1	(129.1)	1,440.1	4,679.7	2.8
Ending Balance (in shares) at Dec. 31, 2017		62,900,000
Consolidated net earnings	470.4				470.0	470.0	0.4
Other comprehensive (loss) earnings	(14.5)			(14.5)		(14.5)
Dividends declared	(116.4)				(116.4)	(116.4)
Issuances of common stock for stock award plans	14.2		14.2			14.2
Issuances of common stock for stock award plans (in shares)		100,000
Shares withheld for employees’ income tax obligations	(11.9)		(11.9)			(11.9)
Repurchases of common stock	$ (100.4)				(100.4)	(100.4)
Repurchases of common stock, Shares	(500,000)	(500,000)
Stock-based compensation expense	$ 29.3		29.3			29.3
Noncontrolling interest acquired in business combination	9.0						9.0
Purchase of the noncontrolling interest in the existing joint venture	(12.8)		(3.6)			(3.6)	(9.2)
Ending Balance at Dec. 31, 2018	$ 4,949.4	$ 0.6	3,396.1	(143.6)	1,693.3	4,946.4	3.0
Ending Balance (in shares) at Dec. 31, 2018	62,500,000	62,500,000
Consolidated net earnings	$ 612.0				611.9	611.9	0.1
Other comprehensive (loss) earnings	(2.2)			(2.2)		(2.2)
Dividends declared	(129.8)				(129.8)	(129.8)
Issuances of common stock for stock award plans	16.7		16.7			16.7
Shares withheld for employees’ income tax obligations	(28.1)		(28.1)			(28.1)
Repurchases of common stock	$ (98.2)				(98.2)	(98.2)
Repurchases of common stock, Shares	(400,000)
Stock-based compensation expense	$ 34.1		34.1			34.1
Distribution to owners of noncontrolling interest	(0.6)						(0.6)
Ending Balance at Dec. 31, 2019	$ 5,353.3	$ 0.6	$ 3,418.8	$ (145.8)	$ 2,077.2	$ 5,350.8	$ 2.5
Ending Balance (in shares) at Dec. 31, 2019	62,400,000	62,400,000

Inventories, Net - Schedule of Inventories Net (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Finished products	$ 643.6	$ 615.7
Products in process	41.9	35.6
Raw materials	32.4	31.3
Supplies and expendable parts	141.5	139.6
Inventories, Gross	859.4	822.2
Less: Allowances	(168.6)	(159.2)
Total	$ 690.8	$ 663.0

Income Taxes - Summary of Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory income tax rate	21.00%	21.00%	35.00%
Effect of statutory depletion	(3.40%)	(3.40%)	(5.60%)
State income taxes, net of federal tax benefit	2.00%	2.80%	1.50%
Change in tax status of subsidiary	(1.70%)
Stock based compensation	(0.50%)	(0.50%)	(1.00%)
Impact from 2017 Tax Act		(3.30%)	(41.70%)
Domestic production deduction			(2.20%)
Other items	0.80%	1.70%	(1.30%)
Effective income tax rate	18.20%	18.30%	(15.30%)

Accounting Policies - Estimated Service Lives for Property, Plant and Equipment (Detail)	12 Months Ended
	Dec. 31, 2019
Building \| Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, Service Lives, Years	5 years
Building \| Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, Service Lives, Years	20 years
Machinery and Equipment \| Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, Service Lives, Years	2 years
Machinery and Equipment \| Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, Service Lives, Years	20 years
Land Improvements \| Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, Service Lives, Years	5 years
Land Improvements \| Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, Service Lives, Years	60 years

Inventories, Net

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Inventories, Net

Note F: Inventories, Net

December 31 (in millions)	2019			2018
Finished products	$	643.6		$	615.7
Products in process		41.9			35.6
Raw materials		32.4			31.3
Supplies and expendable parts		141.5			139.6
		859.4			822.2
Less: Allowances		(168.6	)		(159.2	)
Total	$	690.8		$	663.0

Accounts Receivable, Net - Schedule of Accounts Receivable Net (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Customer receivables	$ 564.4	$ 514.1
Other current receivables	14.0	12.5
Accounts Receivable, gross	578.4	526.6
Less: Allowances	(4.7)	(3.3)
Total	$ 573.7	$ 523.3

Retirement Plans, Postretirement and Postemployment Benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for defined benefit pension plans	$ 878.7	$ 771.9
Combined pension plan and SERP contributions	58.9	162.3
Corporation's matching obligations	$ 17.6	16.5	$ 14.9
Defined contribution plan name	401(a)
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution of pension plans				$ 60.2
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of pension asset equity securities in mid and large capitalization funds	45.00%
Pension
Defined Benefit Plan Disclosure [Line Items]
Prior service cost, recognized in net periodic benefit cost	$ 0.7
Prior service cost, recognized in net periodic benefit cost - deferred tax asset and liability	0.2
Actuarial gain (loss), recognized in net periodic benefit cost	13.5
Actuarial gain (loss), recognized in net periodic benefit cost - deferred tax asset and liability	3.3
Combined pension plan and SERP contributions	58.9	162.3
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service cost, recognized in net periodic benefit cost	0.8
Actuarial gain (loss), recognized in net periodic benefit cost	0.3
Combined pension plan and SERP contributions	2.0	$ 1.0
Prior service cost, recognized in net periodic benefit cost - deferred taxes	0.2
Actuarial gain (loss) , recognized in net periodic benefit cost - deferred taxes	$ 0.1
Postretirement Health Care Plans [Member] \| Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution of pension plans				$ 2.0

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Accumulated Benefit Obligations in Excess of Plan Assets (Detail) - Pension - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 107.1	$ 98.7
Accumulated benefit obligation	96.4	85.5
Fair value of plan assets	$ 0.6	$ 0.6

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 30.8	$ 31.7	$ 26.9
Interest cost	37.6	33.2	36.1
Expected return on assets	(47.9)	(46.0)	(39.8)
Prior service cost (credit)		0.1	0.3
Actuarial (gain) loss	16.0	12.8	14.1
Settlement charge (credit)		2.9
Total net periodic benefit cost (credit)	36.5	34.7	37.6
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1
Interest cost	0.6	0.5	0.7
Prior service cost (credit)	(0.8)	(2.1)	(1.7)
Actuarial (gain) loss	(0.5)	(0.2)	(0.4)
Total net periodic benefit cost (credit)	$ (0.6)	$ (1.7)	$ (1.3)

Segments - Additional Information (Detail) $ in Millions	12 Months Ended
Segments - Additional Information (Detail) $ in Millions	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Reportable business segments \| Segment	3
Asset and portfolio rationalization charge		$ 18.8
Building Materials Business West Group
Segment Reporting Information [Line Items]
Asset and portfolio rationalization charge	$ 18.8

Supplemental Cash Flow Information -Supplemental Disclosures of Cash Flow Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest, net of amount capitalized	$ 127.9	$ 137.2	$ 78.9
Cash paid for income taxes	101.7	$ 28.9	$ 155.8
Operating cash flows used for operating leases	76.1
Operating cash flows used for finance leases	0.5
Financing cash flows used for finance leases	$ 11.0

Revenue Recognition - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue Recognition [Line Items]
Performance obligations, description of timing	Performance obligations within paving service agreements are satisfied over time, primarily ranging from one day to two years. For product revenues and freight revenues, customer payment terms are generally 30 days from invoice date. Customer payments for the paving operations are based on a contractual billing schedule and are due 30 days from invoice date.
Product and freight revenues customer payment terms	30 days
Customer payments terms based on contractual billing	30 days
Future revenues from unsatisfied performance obligations	$ 136.1	$ 78.1	$ 67.0
Service revenues	4,739.1	4,244.3	3,965.6
Revenue recognized from contract liabilities	6.6	6.8
Retainage on contracts	10.2	7.5
Service \| COLORADO
Revenue Recognition [Line Items]
Service revenues	$ 250.6	$ 219.6	$ 245.3
Minimum \| Service
Revenue Recognition [Line Items]
Performance obligations, period	1 day
Maximum \| Service
Revenue Recognition [Line Items]
Performance obligations, period	2 years

Property, Plant and Equipment, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Depreciation, depletion and amortization	$ 354.4	$ 326.1	$ 279.8
Capitalized interest expense	5.1	3.0	$ 3.6
Property, plant and equipment, net	5,206.0	5,157.2
Bahamas And Canada
Property Plant And Equipment [Line Items]
Property, plant and equipment, net	$ 49.7	$ 56.2

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note O: Commitments and Contingencies

Legal and Administrative Proceedings. The Company is engaged in certain legal and administrative proceedings incidental to its normal business activities. In the opinion of management and counsel, based upon currently-available facts, the likelihood is remote that the ultimate outcome of any litigation and other proceedings, including those pertaining to environmental matters (see Note A), relating to the Company and its subsidiaries, will have a material adverse effect on the overall results of the Company’s operations, its cash flows or its financial position.

Asset Retirement Obligations. The Company incurs reclamation and teardown costs as part of its mining and production processes. Estimated future obligations are discounted to their present value and accreted to their projected future obligations via charges to operating expenses. Additionally, the fixed assets recorded concurrently with the liabilities are depreciated over the period until retirement activities are expected to occur. Total accretion and depreciation expenses for 2019, 2018 and 2017 were $9.1 million, $8.0 million and $8.7 million, respectively, and are included in Other operating income and expenses, net, in the consolidated statements of earnings.

The following shows the changes in the asset retirement obligations:

years ended December 31 (in millions)	2019			2018
Balance at beginning of year	$	121.8		$	109.7
Accretion expense		5.6			5.1
Liabilities incurred and liabilities assumed in business combinations		0.6			4.6
Liabilities settled		(1.2	)		(2.8	)
Revisions in estimated cash flows		17.1			5.2
Balance at end of year	$	143.9		$	121.8

Other Environmental Matters. The Company’s operations are subject to and affected by federal, state and local laws and regulations relating to the environment, health and safety and other regulatory matters. Certain of the Company’s operations may, from time to time, involve the use of substances that are classified as toxic or hazardous within the meaning of these laws and regulations. Environmental operating permits are, or may be, required for certain of the Company’s operations, and such permits are subject to modification, renewal and revocation. The Company regularly monitors and reviews its operations, procedures and policies for compliance with these laws and regulations. Despite these compliance efforts, risk of environmental remediation liability is inherent in the operation of the Company’s businesses, as it is with other companies engaged in similar businesses. The Company has no material provisions for environmental remediation liabilities and does not believe such liabilities will have a material adverse effect on the Company in the future.

Insurance Reserves. At December 31, 2019 and 2018, reserves of $39.9 million and $48.3 million, respectively, were recorded for insurance claims.

Letters of Credit. In the normal course of business, the Company provides certain third parties with standby letter of credit agreements guaranteeing its payment for certain insurance claims, contract performance and permit requirements. At December 31, 2019, the Company was contingently liable for $32.9 million in letters of credit.

Surety Bonds. In the normal course of business, at December 31, 2019, the Company was contingently liable for $395.1 million in surety bonds required by certain states and municipalities and their related agencies. The bonds are principally for

certain insurance claims, construction contracts, reclamation obligations and mining permits guaranteeing the Company’s own performance. The Company has indemnified the underwriting insurance company, Liberty Mutual, against any exposure under the surety bonds. In the Company’s past experience, no material claims have been made against these financial instruments.

Borrowing Arrangements with Affiliate. The Company is a co-borrower with an unconsolidated affiliate for a $15.5 million revolving line of credit agreement with Truist Bank, a successor by merger to Suntrust Bank and formerly known as BB&T, of which $11.3 million was outstanding as of December 31, 2019. The line of credit expires in March 2020. The affiliate has agreed to reimburse and indemnify the Company for any payments and expenses the Company may incur from this agreement. The Company holds a lien on the affiliate’s membership interest in a joint venture as collateral for payment under the revolving line of credit.

At December 31, 2019 and 2018, the Company had an interest-only $6.0 million note receivable from the unconsolidated affiliate due December 31, 2022.

Purchase Commitments. The Company had purchase commitments for property, plant and equipment of $93.4 million as of December 31, 2019. The Company also had other purchase obligations related to energy and service contracts of $82.9 million as of December 31, 2019. The Company’s contractual purchase commitments as of December 31, 2019 are as follows:

(in millions)
2020	$	140.6
2021		15.0
2022		3.0
2023		0.9
2024		0.9
Thereafter		15.9
Total	$	176.3

Capital expenditures in 2019, 2018 and 2017 that were purchase commitments as of the prior year end were $106.7 million, $79.3 million and $83.7 million, respectively.

Contracts of Affreightment and Royalty Commitments. Future minimum contracts of affreightment and royalty commitments for all noncancelable agreements as of December 31, 2019 are as follows:

(in millions)	Contracts of Affreightment		Royalty Commitments
2020	$	15.8	$	15.7
2021		16.1		11.1
2022		16.3		10.3
2023		16.6		9.2
2024		16.9		8.9
Thereafter		52.2		59.7
Total	$	133.9	$	114.9

Employees. Approximately 11% of the Company’s employees are represented by a labor union. All such employees are hourly employees. The Company maintains collective bargaining agreements relating to the union employees within the Building Materials business and Magnesia Specialties segment. 100% of the hourly employees of the Magnesia Specialties segment, located in Manistee, Michigan and Woodville, Ohio, are represented by labor unions. The Woodville collective bargaining agreement expires in June 2022. The Manistee collective bargaining agreement expires in August 2023.

Segments (Tables)

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

Financial Data for Continuing Operation for Company's Reportable Segments

The following tables display selected financial data for the Company’s reportable segments. The acquired Bluegrass operations are reported in the Mid-America Group and Southeast Group. Total revenues, as well as the consolidated statements of earnings and comprehensive earnings, reflect the elimination of intersegment revenues.

years ended December 31 (in millions) Total revenues	2019		2018		2017
Mid-America Group	$	1,446.0	$	1,223.2	$	1,053.3
Southeast Group		506.4		423.4		362.6
West Group		2,515.4		2,310.0		2,279.7
Total Building Materials Business		4,467.8		3,956.6		3,695.6
Magnesia Specialties		271.3		287.7		270.0
Total	$	4,739.1	$	4,244.3	$	3,965.6

Gross profit
Mid-America Group	$	482.9	$	366.9	$	335.4
Southeast Group		124.1		77.2		74.6
West Group		473.6		416.2		465.6
Total Building Materials Business		1,080.6		860.3		875.6
Magnesia Specialties		95.4		98.7		89.4
Corporate		3.0		7.6		6.9
Total	$	1,179.0	$	966.6	$	971.9

Selling, general and administrative expenses
Mid-America Group	$	63.1	$	55.8	$	53.9
Southeast Group		21.6		18.7		17.1
West Group		116.3		107.6		102.7
Total Building Materials Business		201.0		182.1		173.7
Magnesia Specialties		11.3		10.0		9.5
Corporate		90.4		88.5		78.9
Total	$	302.7	$	280.6	$	262.1

years ended December 31 (in millions) Earnings (Loss) from operations	2019			2018			2017
Mid-America Group	$	425.9		$	319.1		$	284.8
Southeast Group		103.1			75.9			61.2
West Group		365.2			295.8			360.6
Total Building Materials Business		894.2			690.8			706.6
Magnesia Specialties		83.6			88.1			79.4
Corporate		(92.9	)		(88.2	)		(85.6	)
Total	$	884.9		$	690.7		$	700.4

Earnings from operations for the West Group for 2018 reflect an asset and portfolio rationalization charge of $18.8 million.

December 31 (in millions) Assets employed	2019		2018		2017
Mid-America Group	$	2,879.3	$	2,788.5	$	1,532.9
Southeast Group		1,442.5		1,299.5		616.3
West Group		5,320.7		4,989.6		5,014.2
Total Building Materials Business		9,642.5		9,077.6		7,163.4
Magnesia Specialties		176.2		156.1		152.3
Corporate		312.9		317.7		1,676.8
Total	$	10,131.6	$	9,551.4	$	8,992.5

years ended December 31 (in millions) Depreciation, depletion and amortization	2019		2018		2017
Mid-America Group	$	110.2	$	93.6	$	69.7
Southeast Group		47.8		41.2		30.8
West Group		183.3		180.9		169.8
Total Building Materials Business		341.3		315.7		270.3
Magnesia Specialties		10.2		10.4		10.1
Corporate		20.0		17.9		16.8
Total	$	371.5	$	344.0	$	297.2

Total property additions, including the impact of acquisitions
Mid-America Group	$	127.7	$	1,157.1	$	139.5
Southeast Group		45.3		603.1		34.6
West Group		182.6		148.1		240.8
Total Building Materials Business		355.6		1,908.3		414.9
Magnesia Specialties		20.0		12.5		11.1
Corporate		12.0		4.8		12.6
Total	$	387.6	$	1,925.6	$	438.6

years ended December 31 (in millions) Property additions through acquisitions	2019		2018		2017
Mid-America Group	$	—	$	980.3	$	0.1
Southeast Group		—		561.5		—
West Group		—		1.4		2.4
Total Building Materials Business		—		1,543.2		2.5
Magnesia Specialties		—		—		—
Corporate		—		—		—
Total	$	—	$	1,543.2	$	2.5

Accounts Receivable, Net - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Due from unconsolidated affiliates	$ 2.9	$ 2.5

Shareholders' Equity

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Shareholders' Equity

Note N: Shareholders’ Equity

The authorized capital structure of the Company includes 100.0 million shares of common stock, with a par value of $0.01 a share. At December 31, 2019, approximately 1.5 million common shares were reserved for issuance under stock-based award plans.

Pursuant to authority granted by its Board of Directors, the Company can repurchase up to 20.0 million shares of common stock. The Company repurchased 0.4 million, 0.5 million and 0.5 million shares of common stock during 2019, 2018 and 2017, respectively. At December 31, 2019, 13.7 million shares of common stock were remaining under the Company’s repurchase authorization.

Accounting Policies - Components of Changes in Accumulated Other Comprehensive Loss and Related Cumulative Noncurrent Deferred Tax Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 4,949.4	$ 4,682.5	$ 4,142.6
Other comprehensive (loss) earnings before reclassifications, net of Tax	(13.3)	(25.0)	(6.9)
Amounts reclassified from accumulated other comprehensive loss, net of tax	11.1	10.5	8.5
Other comprehensive (loss) earnings, net of tax	(2.2)	(14.5)	1.6
Ending Balance	5,353.3	4,949.4	4,682.5
Cumulative noncurrent deferred tax assets at end of period	85.2	84.2	80.1
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(141.5)	(128.8)	(128.4)
Other comprehensive (loss) earnings before reclassifications, net of Tax	(14.5)	(22.9)	(8.1)
Amounts reclassified from accumulated other comprehensive loss, net of tax	11.1	10.2	7.7
Other comprehensive (loss) earnings, net of tax	(3.4)	(12.7)	(0.4)
Ending Balance	(144.9)	(141.5)	(128.8)
Cumulative noncurrent deferred tax assets at end of period	85.2	84.2	79.9
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2.1)		(1.2)
Other comprehensive (loss) earnings before reclassifications, net of Tax	1.2	(2.1)	1.2
Other comprehensive (loss) earnings, net of tax	1.2	(2.1)	1.2
Ending Balance	(0.9)	(2.1)
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(0.3)	(1.1)
Amounts reclassified from accumulated other comprehensive loss, net of tax		0.3	0.8
Other comprehensive (loss) earnings, net of tax		0.3	0.8
Ending Balance			(0.3)
Cumulative noncurrent deferred tax assets at end of period			0.2
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(143.6)	(129.1)	(130.7)
Other comprehensive (loss) earnings before reclassifications, net of Tax	(13.3)
Ending Balance	$ (145.8)	$ (143.6)	$ (129.1)

Revenue Recognition - Schedule of Company's Total Revenues by Category for each Reportable Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue Recognition [Line Items]
Total	$ 4,739.1	$ 4,244.3	$ 3,965.6
Building Materials Business
Revenue Recognition [Line Items]
Total	4,467.8	3,956.6	3,695.6
Products and Services
Revenue Recognition [Line Items]
Total	4,422.3	3,980.4	3,723.5
Products and Services \| Building Materials Business
Revenue Recognition [Line Items]
Total	4,172.4	3,711.8	3,470.8
Freight
Revenue Recognition [Line Items]
Total	316.8	263.9	242.1
Freight \| Building Materials Business
Revenue Recognition [Line Items]
Total	295.4	244.8	224.8
Operating Segments \| Building Materials Business
Revenue Recognition [Line Items]
Total	4,467.8	3,956.6	3,695.6
Operating Segments \| Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	1,446.0	1,223.2	1,053.3
Operating Segments \| Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	506.4	423.4	362.6
Operating Segments \| Building Materials Business West Group
Revenue Recognition [Line Items]
Total	2,515.4	2,310.0	2,279.7
Operating Segments \| Magnesia Specialties
Revenue Recognition [Line Items]
Total	271.3	287.7	270.0
Operating Segments \| Products and Services \| Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	1,328.8	1,133.8	982.2
Operating Segments \| Products and Services \| Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	489.1	409.6	348.7
Operating Segments \| Products and Services \| Building Materials Business West Group
Revenue Recognition [Line Items]
Total	2,354.5	2,168.4	2,139.9
Operating Segments \| Products and Services \| Magnesia Specialties
Revenue Recognition [Line Items]
Total	249.9	268.6	252.7
Operating Segments \| Freight \| Building Materials Business
Revenue Recognition [Line Items]
Total	295.4	244.8	224.8
Operating Segments \| Freight \| Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	117.2	89.4	71.1
Operating Segments \| Freight \| Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	17.3	13.8	13.9
Operating Segments \| Freight \| Building Materials Business West Group
Revenue Recognition [Line Items]
Total	160.9	141.6	139.8
Operating Segments \| Freight \| Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 21.4	$ 19.1	$ 17.3

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Assumed Health Care Cost Trend Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Health care cost trend rate assumed for next year	6.75%	7.00%
Rate to which the cost trend rate gradually declines	4.75%	5.00%
Year the rate reaches the ultimate rate	2028	2023

Revenue Recognition - Summary of Information About the Company's Contract Balances (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Revenue From Contract With Customer [Abstract]
Costs in excess of billings	$ 2.8	$ 2.0
Billings in excess of costs	$ 7.8	$ 6.7

Supplemental Cash Flow Information (Tables)

12 Months Ended

Dec. 31, 2019

Supplemental Cash Flow Elements [Abstract]

Schedule Of Other Significant Noncash Transactions

Noncash investing and financing activities are as follows:

years ended December 31
(in millions)	2019		2018		2017
Accrued liabilities for purchases of property, plant and equipment	$	54.2	$	67.0	$	61.6
Acquisition of assets through asset exchange	$	2.4	$	—	$	2.5
Remeasurement of operating lease right-of-use assets	$	2.0	$	—	$	—
Right-of-use assets obtained in exchange for new operating lease liabilities	$	45.7	$	—	$	—
Right-of-use assets obtained in exchange for new finance lease liabilities	$	0.2	$	—	$	—
Acquisition of assets through capital lease	$	—	$	1.1	$	0.8
Sale of asset to settle liability	$	—	$	—	$	0.9

Supplemental Disclosures of Cash Flow Information

Supplemental disclosures of cash flow information are as follows:

years ended December 31
(in millions)	2019		2018		2017
Cash paid for interest, net of amount capitalized	$	127.9	$	137.2	$	78.9
Cash paid for income taxes	$	101.7	$	28.9	$	155.8
Cash paid for amounts included in the measurement of lease liabilities¹:
Operating cash flows used for operating leases	$	76.1
Operating cash flows used for finance leases	$	0.5
Financing cash flows used for finance leases	$	11.0

¹	These disclosures are required by ASC 842, which was adopted on January 1, 2019.

Business Combinations - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Combinations [Line Items]
Total revenues		$ 4,739.1	$ 4,244.3	$ 3,965.6
Earnings from operations		884.9	690.7	700.4
Acquisition-related expenses		0.5	13.5	8.6
Bluegrass Materials Company
Business Combinations [Line Items]
Date of acquisition	2018-04
Business acquisition in cash	$ 1,600.0
Total revenues		245.7	172.0
Earnings from operations		$ 70.5	32.4
Acquisition-related expenses			28.3	8.6
Gain on a required divestiture of a legacy quarry			$ 14.8
Gain on sale of business				14.8
Increase in cost of revenues				18.7
Bluegrass Materials Company \| Pro Forma
Business Combinations [Line Items]
Acquisition-related expenses				$ 28.1

Long-Term Debt - Additional Information (Detail) - USD ($)			12 Months Ended
	Dec. 20, 2018	Dec. 05, 2016	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Required offer price to repurchase senior notes if change of control repurchase event and downgrade below investment grade credit rating occurs			101.00%
Maximum consolidated debt reduction for unrestricted cash and cash equivalents for debt covenant calculation			$ 200,000,000.0
Outstanding letters of credit			32,900,000
Minimum
Debt Instrument [Line Items]
Reduction of consolidated debt in the debt ratio calculation			$ 50,000,000.0
Including Acquisition Bridge Debt \| Maximum
Debt Instrument [Line Items]
Debt covenant			3.50
Excluding Acquisition Bridge Debt \| Maximum
Debt Instrument [Line Items]
Debt covenant			3.75
Revolving Facility
Debt Instrument [Line Items]
Credit facility commitment		$ 700,000,000.0	$ 697,700,000
Senior unsecured revolving facility, maturity period		5 years
Debt instrument maturity period			Dec. 05, 2024
Debt instrument extended maturity period	1 year
Outstanding letters of credit			$ 2,300,000	$ 2,300,000
Borrowings under revolving facility		$ 700,000,000.0	697,700,000
Short-term Line of Credit
Debt Instrument [Line Items]
Credit facility commitment			5,000,000.0
Borrowings under revolving facility			5,000,000.0
Outstanding borrowing under credit facility			$ 0	$ 0
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Interest rate on notes			4.25%
Maturity year			2024
Maturity date			Jul. 02, 2024
7% Debentures, Due 2025
Debt Instrument [Line Items]
Interest rate on notes			7.00%
Maturity year			2025
Maturity date			Dec. 01, 2025
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Interest rate on notes			3.45%
Maturity year			2027
Maturity date			Jun. 01, 2027
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Interest rate on notes			3.50%
Maturity year			2027
Maturity date			Dec. 15, 2027
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Interest rate on notes			6.25%
Maturity year			2037
Maturity date			May 01, 2037
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Interest rate on notes			4.25%
Maturity year			2047
Maturity date			Dec. 15, 2047
Floating Rate Senior Notes, Due 2020
Debt Instrument [Line Items]
Maturity year			2020
Maturity date			May 22, 2020
Trade Receivable Facility
Debt Instrument [Line Items]
Credit facility commitment			$ 400,000,000.0
Debt instrument maturity period			Sep. 23, 2020
Borrowings under revolving facility			$ 400,000,000.0
Trade Receivable Facility \| London Interbank Offered Rate(LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate			0.725%

Leases - Summary of Components of Lease Cost (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 80.9
Finance lease cost:
Amortization of right-of-use assets	3.4
Interest on lease liabilities	0.5
Variable lease cost	21.1
Short-term lease cost	33.0
Total lease cost	$ 138.9

Financial Instruments

12 Months Ended

Dec. 31, 2019

Financial Instruments Disclosure [Abstract]

Financial Instruments

Note I: Financial Instruments

The Company’s financial instruments include temporary cash investments, accounts receivable, notes receivable, accounts payable, publicly-registered long-term notes, debentures and other long-term debt.

Temporary cash investments are placed primarily in money market funds, money market demand deposit accounts or offshore time deposit accounts with financial institutions. The Company’s cash equivalents have maturities of less than three months. Due to the short maturity of these investments, they are carried on the consolidated balance sheets at cost, which approximates fair value.

Accounts receivable are due from a large number of customers, primarily in the construction industry, and are dispersed across wide geographic and economic regions. However, accounts receivable are more heavily concentrated in certain states,

namely Texas, Colorado, North Carolina, Georgia and Iowa. The estimated fair values of accounts receivable approximate their carrying amounts.

Notes receivable are primarily promissory notes with customers and are not publicly traded. Management estimates that the fair value of notes receivable approximates its carrying amount.

Accounts payable represent amounts owed to suppliers and vendors. The estimated fair value of accounts payable approximates its carrying amount due to the short-term nature of the payables.

The carrying values and fair values of the Company’s long-term debt were $2.77 billion and $2.94 billion, respectively, at December 31, 2019 and $3.12 billion and $3.01 billion, respectively, at December 31, 2018. The estimated fair value of the Company’s publicly-registered long-term debt was estimated based on Level 2 of the fair value hierarchy using quoted market prices. The estimated fair values of other borrowings, which primarily represent variable-rate debt, approximate their carrying amounts as the interest rates reset periodically.

Retirement Plans, Postretirement and Postemployment Benefits - Net Periodic Benefit Cost Recognized in Comprehensive Earnings (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	$ 1.0	$ (1.7)	$ 1.2
Pension
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	11.7	32.1	13.3
Net prior service cost (credit)	6.4
Prior service (cost) credit		(0.1)	(0.3)
Actuarial gain (loss)	(16.0)	(12.8)	(14.1)
Settlement (charge) credit		(2.9)
Total	2.1	16.3	(1.1)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net prior service cost (credit)			(3.9)
Prior service (cost) credit	0.8	2.1	1.7
Actuarial gain (loss)	0.5	0.2	0.4
Total	$ 2.3	$ 0.6	$ (0.6)

Segments - Financial Data for Continuing Operations for Company's Reportable Segments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 4,739.1	$ 4,244.3	$ 3,965.6
Gross profit	1,179.0	966.6	971.9
Selling, general and administrative expenses	302.7	280.6	262.1
Earnings (Loss) from operations	884.9	690.7	700.4
Assets employed	10,131.6	9,551.4	8,992.5
Depreciation, depletion and amortization	371.5	344.0	297.2
Total property additions, including the impact of acquisitions	387.6	1,925.6	438.6
Property additions through acquisitions		1,543.2	2.5
Building Materials Business
Segment Reporting Information [Line Items]
Total revenues	4,467.8	3,956.6	3,695.6
Gross profit	1,080.6	860.3	875.6
Selling, general and administrative expenses	201.0	182.1	173.7
Earnings (Loss) from operations	894.2	690.8	706.6
Assets employed	9,642.5	9,077.6	7,163.4
Depreciation, depletion and amortization	341.3	315.7	270.3
Total property additions, including the impact of acquisitions	355.6	1,908.3	414.9
Property additions through acquisitions		1,543.2	2.5
Operating Segments \| Building Materials Business Mid-America Group
Segment Reporting Information [Line Items]
Total revenues	1,446.0	1,223.2	1,053.3
Gross profit	482.9	366.9	335.4
Selling, general and administrative expenses	63.1	55.8	53.9
Earnings (Loss) from operations	425.9	319.1	284.8
Assets employed	2,879.3	2,788.5	1,532.9
Depreciation, depletion and amortization	110.2	93.6	69.7
Total property additions, including the impact of acquisitions	127.7	1,157.1	139.5
Property additions through acquisitions		980.3	0.1
Operating Segments \| Building Materials Business Southeast Group
Segment Reporting Information [Line Items]
Total revenues	506.4	423.4	362.6
Gross profit	124.1	77.2	74.6
Selling, general and administrative expenses	21.6	18.7	17.1
Earnings (Loss) from operations	103.1	75.9	61.2
Assets employed	1,442.5	1,299.5	616.3
Depreciation, depletion and amortization	47.8	41.2	30.8
Total property additions, including the impact of acquisitions	45.3	603.1	34.6
Property additions through acquisitions		561.5
Operating Segments \| Building Materials Business West Group
Segment Reporting Information [Line Items]
Total revenues	2,515.4	2,310.0	2,279.7
Gross profit	473.6	416.2	465.6
Selling, general and administrative expenses	116.3	107.6	102.7
Earnings (Loss) from operations	365.2	295.8	360.6
Assets employed	5,320.7	4,989.6	5,014.2
Depreciation, depletion and amortization	183.3	180.9	169.8
Total property additions, including the impact of acquisitions	182.6	148.1	240.8
Property additions through acquisitions		1.4	2.4
Operating Segments \| Building Materials Business
Segment Reporting Information [Line Items]
Total revenues	4,467.8	3,956.6	3,695.6
Gross profit	1,080.6	860.3	875.6
Operating Segments \| Magnesia Specialties
Segment Reporting Information [Line Items]
Total revenues	271.3	287.7	270.0
Gross profit	95.4	98.7	89.4
Selling, general and administrative expenses	11.3	10.0	9.5
Earnings (Loss) from operations	83.6	88.1	79.4
Assets employed	176.2	156.1	152.3
Depreciation, depletion and amortization	10.2	10.4	10.1
Total property additions, including the impact of acquisitions	20.0	12.5	11.1
Corporate
Segment Reporting Information [Line Items]
Gross profit	3.0	7.6	6.9
Selling, general and administrative expenses	90.4	88.5	78.9
Earnings (Loss) from operations	(92.9)	(88.2)	(85.6)
Assets employed	312.9	317.7	1,676.8
Depreciation, depletion and amortization	20.0	17.9	16.8
Total property additions, including the impact of acquisitions	$ 12.0	$ 4.8	$ 12.6

Leases - Summary of Future Minimum Lease and Royalty Commitments for all Noncancelable Agreements and Capital Lease Obligations (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Capital Leases
2019		$ 3.7
2020		2.7
2021		1.7
2022		1.0
2023		0.7
Thereafter		3.9
Total		13.7
Less: imputed interest		(2.9)
Present value of minimum lease payments		10.8
Less: current capital lease obligations		(3.2)
Long-term capital lease obligations		7.6
Operating Leases
2019		106.0
2020		70.5
2021		60.4
2022		57.5
2023		56.5
Thereafter		318.1
Total		669.0
Royalty Commitments
2019		14.6
2020		11.4
2021		10.3
2022		9.5
2023		8.1
Thereafter		66.0
Total	$ 114.9	$ 119.9

Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) Facility State Plant shares	Dec. 31, 2018 shares	Dec. 31, 2017 shares	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Number of states with aggregates business sales by destination \| State	27
Number of cement plants \| Plant	2
Number of asphalt plants \| Plant	7
Out of period expenses	$ 15.7
Retirement plans and postretirement benefits amortized amount representing percentage of greater of projected benefit obligation or pension plan assets.	10.00%
Minimum likelihood for recognition of tax benefit related to uncertain tax position	50.00%
Operating lease, right of use asset	$ 481.9
Operating lease, liability	486.6
Finance leases, right of use asset	18.3
Finance leases, liability	$ 8.7
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating lease, right of use asset				$ 502.5
Operating lease, liability				501.6
Finance leases, right of use asset				10.9
Finance leases, liability				$ 12.1
Stock Options
Significant Accounting Policies [Line Items]
Stock options issued \| shares	0	0	0
Expendable Parts Inventory
Significant Accounting Policies [Line Items]
Allowance for inventories in excess of sales requisite Record period	5 years
Supplies Inventory
Significant Accounting Policies [Line Items]
Allowance for inventories in excess of sales requisite Record period	1 year
Minimum
Significant Accounting Policies [Line Items]
Number of quarries and yards \| Facility	300
Number of ready mixed concrete plants \| Plant	141
Minimum \| Inventory Finished Goods
Significant Accounting Policies [Line Items]
Allowance for inventories in excess of sales requisite Record period	12 months
Maximum
Significant Accounting Policies [Line Items]
Warranty term	1 year
Maximum \| Inventory Finished Goods
Significant Accounting Policies [Line Items]
Allowance for inventories in excess of sales requisite Record period	5 years
Percentage of Aggregates Business Net Sales in Top Five Sales states \| Geographic Concentration Risk \| Sales Revenue Segment
Significant Accounting Policies [Line Items]
Total net sales, percentage	72.00%

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Change In Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Balance at beginning of year	$ 717.9
Employer contributions	58.9	$ 162.3
Balance at end of year	868.0	717.9
Pension
Defined Benefit Plan Disclosure [Line Items]
Balance at beginning of year	717.9	638.1
Actual return on plan assets, net	131.3	(40.8)
Employer contributions	58.9	162.3
Gross benefits paid	(40.1)	(41.7)
Balance at end of year	868.0	717.9
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	2.0	1.0
Participants' contributions	1.2	0.3
Gross benefits paid	$ (3.2)	$ (1.3)

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Expected Benefit Payments (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Pension
Defined Benefit Plan Disclosure [Line Items]
2020	$ 43.5
2021	44.8
2022	46.2
2023	47.6
2024	50.9
Years 2025 - 2029	271.0
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
2020	2.0
2021	1.4
2022	1.4
2023	1.3
2024	1.2
Years 2025 - 2029	$ 4.7

Business Combinations

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

Business Combinations

Note D: Business Combinations

In April 2018, the Company acquired Bluegrass Materials Company (“Bluegrass”), the then-largest privately-held, pure-play aggregates company in the United States, for $1.6 billion. Bluegrass’ operations included 22 active sites with more than 125 years of reserves, collectively, in Georgia, South Carolina, Tennessee, Maryland, Kentucky and Pennsylvania. These operations complement the Company’s existing southeastern footprint in its Mid-America and Southeast Groups and provide a new growth platform within Maryland and Kentucky.

The Company determined fair values of the assets acquired and liabilities assumed. As of April 2019, the measurement period is closed. The following is a summary of the estimated fair values of the assets acquired and the liabilities assumed as of the acquisition date:

(in millions)
Assets:
Cash and cash equivalents	$	1.2
Receivables		25.5
Inventory		46.6
Other current assets		1.0
Property, plant and equipment		1,519.3
Intangible assets, other than goodwill		20.2
Goodwill		243.0
Total Assets		1,856.8
Liabilities:
Accounts payable and accrued expenses		17.9
Deferred income tax liabilities, net		212.5
Noncontrolling interest		9.0
Total Liabilities		239.4
Total Consideration	$	1,617.4

Goodwill represents the excess purchase price over the fair values of assets acquired and liabilities assumed and reflects projected operating synergies from the transaction, including expected overhead savings. None of the goodwill generated by the transaction will be deductible for income tax purposes.

Total revenues and earnings from operations attributable to acquired operations included in the consolidated statements of earnings were $245.7 million and $70.5 million, respectively, for the year ended December 31, 2019, and $172.0 million and $32.4 million, respectively, for the year ended December 31, 2018.

Acquisition-related expenses, primarily related to Bluegrass, were $28.3 million and $8.6 million for the years ended December 31, 2018 and 2017, respectively. Acquisition-related expenses, net, for 2018 also include a $14.8 million gain on a required divestiture of a legacy quarry.

Unaudited Pro Forma Financial Information

The unaudited pro forma financial information summarizes the combined results of operations for the Company and Bluegrass as though the companies were combined as of January 1, 2017. Financial information for periods prior to the April 2018 acquisition date included in the pro forma earnings does not reflect any cost savings or associated costs to achieve such savings from operating efficiencies or synergies that result from the combination. Consistent with the assumed acquisition date of January 1, 2017, the pro forma financial results for the year ended December 31, 2017 include acquisition-related expenses of $28.1 million, the $14.8 million gain on the required divestiture of assets and the one-time $18.7 million increase in cost of revenues for the sale of acquired inventory marked up to fair value as part of acquisition accounting.

The pro forma information does not purport to project the future financial position or operating results of the combined company. The pro forma financial information as presented below is for informational purposes only and is not indicative of the results of operations that would have been achieved if the acquisition had taken place at the beginning of fiscal year 2017.

years ended December 31
(in millions, except for per share data)	2018		2017
Total revenues	$	4,299.7	$	4,178.6
Net earnings attributable to Martin Marietta	$	489.5	$	691.7
Diluted earnings per share	$	7.75	$	10.94

In August 2018, the Company purchased the remaining noncontrolling interest in a consolidated joint venture where the controlling interest was acquired as part of the Bluegrass acquisition.

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Funded Status (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Funded status of the plan at end of year	$ (109.8)	$ (130.0)
Accrued benefit cost	(109.8)	(130.0)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Funded status of the plan at end of year	(13.0)	(13.3)
Accrued benefit cost	$ (13.0)	$ (13.3)

Income Taxes - Schedule of Unrecognized Tax Benefits Excluding Interest Correlative Effects (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at beginning of year	$ 24.1	$ 22.4	$ 21.8
Gross increases – tax positions in prior years	0.4	0.9	1.4
Gross decreases – tax positions in prior years			(0.7)
Gross increases – tax positions in current year	1.8	1.8	5.0
Gross decreases – tax positions in current year	(0.8)	(1.0)	(0.9)
Lapse of statute of limitations			(4.2)
Unrecognized tax benefits at end of year	25.5	24.1	22.4
Amount that, if recognized, would favorably impact the effective tax rate	$ 15.5	$ 12.8	$ 10.4

Stock-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note L: Stock-Based Compensation

On May 19, 2016, the Company’s shareholders approved the Martin Marietta Amended and Restated Stock-Based Award Plan. The Martin Marietta Materials, Inc. Stock-Based Award Plan, as amended from time to time, along with the Amended Omnibus Securities Award Plan, originally approved in 1994 (collectively, the Plans), are still effective for awards made prior to 2017. The Company has been authorized by the Board of Directors to repurchase shares of the Company’s common stock for issuance under the stock-based award plans (see Note N).

The Company grants restricted stock awards under the Plans to a group of executive officers, key personnel and nonemployee members of the Board of Directors. The vesting of certain restricted stock awards is based on certain performance criteria over a specified period of time. The number of shares may be increased to the maximum or reduced to the minimum threshold based on the results of those criteria. In addition, certain awards are granted to individuals to encourage retention and motivate key employees. These awards generally vest if the employee is continuously employed over a specified period of time and require no payment from the employee. Awards granted to nonemployee members of the Board of Directors vest immediately.

The fair value of stock-based award grants is expensed over the vesting period. Awards to employees eligible for retirement prior to the award becoming fully vested are expensed over the period through the date that the employee first becomes eligible to retire and is no longer required to provide service to earn the award. Awards granted to nonemployee members of the Board of Directors are expensed immediately.

Additionally, an incentive compensation stock plan has been adopted under the Plans whereby certain participants may elect to use up to 50% of their annual incentive compensation to acquire units representing shares of the Company’s common stock at a 20% discount to the market value on the date of the incentive compensation award. Certain executive officers are required to participate in the incentive compensation stock plan at certain minimum levels. Participants receive unrestricted shares of common stock in an amount equal to their respective units generally at the end of a 34-month period of additional employment from the date of award or at retirement beginning at age 62. All rights of ownership of the common stock convey to the participants upon the issuance of their respective shares at the end of the ownership-vesting period.

The following table summarizes information for restricted stock awards and incentive compensation stock awards for 2019:

	Restricted Stock - Service Based					Restricted Stock - Performance Based					Incentive Compensation Stock
	Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value
January 1, 2019		278,147		$	158.29		151,939		$	174.74		35,376		$	206.55
Awarded		86,922		$	196.91		49,644		$	192.27		21,883		$	192.27
Distributed		(171,689	)	$	148.72		(54,424	)	$	133.73		(15,948	)	$	206.23
Forfeited		(9,441	)	$	166.51		(5,329	)	$	205.21		(1,727	)	$	205.54
Adjustment for performance		—		$	—		(17,609	)	$	133.77		—		$	—
December 31, 2019		183,939		$	185.06		124,221		$	204.21		39,584		$	198.83

The weighted-average grant-date fair value of service-based restricted stock awards granted during 2019, 2018 and 2017 was $196.91, $211.03 and $213.76, respectively. The weighted-average grant-date fair value of performance-based restricted stock awards granted during 2019, 2018 and 2017 was $192.27, $212.12 and $207.73, respectively. The weighted-average grant-date fair value of incentive compensation stock awards granted during 2019, 2018 and 2017 was $192.27, $212.12 and $208.68, respectively.

The aggregate intrinsic values for unvested restricted stock awards and unvested incentive compensation stock awards at December 31, 2019 were $86.2 million and $4.8 million, respectively, and were based on the closing price of the Company’s common stock at December 31, 2019, which was $279.64. The aggregate intrinsic values of restricted stock awards distributed during the years ended December 31, 2019, 2018 and 2017 were $49.8 million, $23.0 million and $15.8 million, respectively. The aggregate intrinsic values of incentive compensation stock awards distributed during the years ended December 31, 2019, 2018 and 2017 were $1.5 million, $1.7 million and $2.6 million, respectively. The aggregate intrinsic values for distributed awards were based on the closing prices of the Company’s common stock on the dates of distribution.

Under the Plans, prior to 2016, the Company granted options to employees to purchase its common stock at a price equal to the closing market value at the date of grant. Options become exercisable in four annual installments beginning one year after date of grant. Options granted starting in 2013 expire ten years after the grant date while outstanding options granted prior to 2013 expire eight years after the grant date.

In connection with the TXI acquisition, completed in 2014, the Company issued 821,282 Martin Marietta stock options (Replacement Options) to holders of outstanding TXI stock options at the acquisition date. The Company issued 0.7 Replacement Options for each outstanding TXI stock option, and the Replacement Option prices reflected the exchange ratio. The Replacement Options will expire on the original contractual dates when the TXI stock options were initially issued. Consistent with the terms of the Company’s other outstanding stock options, Replacement Options expire 90 days after employment is terminated.

The following table includes summary information for stock options as of December 31, 2019:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (years)
Outstanding at January 1, 2019		210,390		$	95.93
Exercised		(150,722	)	$	90.86
Terminated		(828	)	$	94.75
Outstanding at December 31, 2019		58,840		$	108.93		3.1

Exercisable at December 31, 2019		58,840		$	108.93		3.1

The aggregate intrinsic values of options exercised during the years ended December 31, 2019, 2018 and 2017 were $21.6 million, $12.4 million and $13.2 million, respectively, and were based on the closing prices of the Company’s common stock on the dates of exercise. The aggregate intrinsic values for options outstanding and exercisable at December 31, 2019 were $10.0 million and were based on the closing price of the Company’s common stock at December 31, 2019, which was $279.64. The excess tax benefits for stock options exercised during the years ended December 31, 2019, 2018 and 2017 were $2.0 million, $1.7 million and $3.5 million, respectively.

At December 31, 2019, there are approximately 742,000 awards available for grant under the Plans. In 2016, the Company’s shareholders approved the issuance of an additional 800,000 shares of common stock under the Plans. As part of approving the shares, the Company agreed to not issue any additional awards under the legacy TXI plan. The awards available for grant under the Plans at December 31, 2019 reflect no awards available under the legacy TXI plan.

In 1996, the Company adopted the Shareholder Value Achievement Plan to award shares of the Company’s common stock to key senior employees based on certain common stock performance criteria over a long-term period. Under the terms of this plan, 250,000 shares of common stock were reserved for issuance. Through December 31, 2019, 42,025 shares have been issued under this plan. No awards have been granted under this plan since 2000.

The Company adopted and the shareholders approved the Common Stock Purchase Plan for Directors in 1996, which provides nonemployee members of the Board of Directors the election to receive all or a portion of their total fees in the form of the Company’s common stock. Beginning in 2016, members of the Board of Directors were not required to defer any of their fees in the form of the Company’s common stock. Under the terms of this plan, 300,000 shares of common stock were reserved for issuance. Nonemployee members of the Board of Directors elected to defer portions of their fees representing 2,756, 3,105 and 2,132 shares of the Company’s common stock under this plan during 2019, 2018 and 2017, respectively.

The following table summarizes stock-based compensation expense for the years ended December 31, 2019, 2018 and 2017, unrecognized compensation cost for nonvested awards at December 31, 2019 and the weighted-average period over which unrecognized compensation cost will be recognized:

(in millions, except year data)	Stock Options		Restricted Stock		Incentive Compensation Stock		Directors’ Awards		Total
Stock-based compensation expense recognized for years ended December 31:
2019	$	0.1	$	32.6	$	0.8	$	0.6	$	34.1
2018	$	0.3	$	27.7	$	0.7	$	0.6	$	29.3
2017	$	0.7	$	28.7	$	0.7	$	0.4	$	30.5
Unrecognized compensation cost at December 31, 2019	$	—	$	22.7	$	0.5	$	—	$	23.2
Weighted-average period over which unrecognized compensation cost will be recognized			2.1 years		1.7 years

The following presents expected stock-based compensation expense in future periods for outstanding awards as of December 31, 2019:

(in millions)
2020	$	14.9
2021		7.2
2022		0.8
2023		0.3
Total	$	23.2

Stock-based compensation expense is included in selling, general and administrative expenses in the Company’s consolidated statements of earnings.

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.69%	4.38%
Rate of increase in future compensation levels	4.50%	4.50%
Discount rate	4.38%	3.76%	4.29%
Rate of increase in future compensation levels	4.50%	4.50%	4.50%
Expected long-term rate of return on assets	6.75%	6.75%	6.75%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.29%	4.15%
Discount rate	4.15%	3.47%	3.78%

Accounts Receivable, Net

12 Months Ended

Dec. 31, 2019

Receivables [Abstract]

Accounts Receivable, Net

Note E: Accounts Receivable, Net

December 31
(in millions)	2019			2018
Customer receivables	$	564.4		$	514.1
Other current receivables		14.0			12.5
		578.4			526.6
Less: Allowances		(4.7	)		(3.3	)
Total	$	573.7		$	523.3

Of the total accounts receivable, net, balances, $2.9 million and $2.5 million at December 31, 2019 and 2018, respectively, were due from unconsolidated affiliates.

Income Taxes - Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal income taxes:
Current	$ 83.9	$ 15.3	$ 129.2
Deferred	31.1	69.6	(239.3)
Total federal income taxes	115.0	84.9	(110.1)
State income taxes:
Current	20.5	6.0	14.8
Deferred	(1.5)	14.1	(0.9)
Total state income taxes	19.0	20.1	13.9
Foreign income taxes:
Current	2.8	(1.4)	1.2
Deferred	(0.5)	2.1	0.5
Total foreign income taxes	2.3	0.7	1.7
Income tax expense (benefit)	$ 136.3	$ 105.7	$ (94.5)

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2018
Commitments and Contingencies [Line Items]
Asset retirement obligation depreciation and accretion	$ 9,100,000	$ 8,000,000.0	$ 8,700,000
Liability reserve for insurance claims	39,900,000	48,300,000
Outstanding letters of credit	32,900,000
Surety bonds	395,100,000
Due from affiliate	11,300,000
Guarantee of affiliate's obligations				$ 15,500,000
Purchase commitments for property, plant and equipment	176,300,000
Capital expenditures	$ 106,700,000	79,300,000	$ 83,700,000
Percentage of employees represented in labor union	11.00%
Woodville
Commitments and Contingencies [Line Items]
Collective bargaining agreement expiration month year	2022-06
Magnesia Specialties
Commitments and Contingencies [Line Items]
Percentage of employees represented in labor union	100.00%
Collective bargaining agreement expiration month year	2023-08
Capital Addition Purchase Commitments
Commitments and Contingencies [Line Items]
Purchase commitments for property, plant and equipment	$ 93,400,000
Energy And Service Contracts
Commitments and Contingencies [Line Items]
Purchase commitments for property, plant and equipment	82,900,000
Interest-only loan
Commitments and Contingencies [Line Items]
Due from affiliate	$ 6,000,000.0	$ 6,000,000.0
Maturity date	Dec. 31, 2022	Dec. 31, 2022
Revolving Line Of Credit Expires In August 2015
Commitments and Contingencies [Line Items]
Line of credit maturity period	2020-03
Revolving Facility
Commitments and Contingencies [Line Items]
Outstanding letters of credit	$ 2,300,000	$ 2,300,000

Revenue Recognition - Additional Information (Detail 1)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Minimum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-01-01
Revenue Recognition [Line Items]
Performance obligations, customer satisfaction period			1 month
Minimum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue Recognition [Line Items]
Performance obligations, customer satisfaction period		2 months
Minimum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Recognition [Line Items]
Performance obligations, customer satisfaction period	3 months
Maximum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-01-01
Revenue Recognition [Line Items]
Performance obligations, customer satisfaction period			23 months
Maximum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue Recognition [Line Items]
Performance obligations, customer satisfaction period		22 months
Maximum \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Recognition [Line Items]
Performance obligations, customer satisfaction period	12 months

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Components of Income Tax Expense (Benefit)

The components of the Company’s income tax expense (benefit) are as follows:

years ended December 31 (in millions)	2019			2018			2017
Federal income taxes:
Current	$	83.9		$	15.3		$	129.2
Deferred		31.1			69.6			(239.3	)
Total federal income taxes		115.0			84.9			(110.1	)
State income taxes:
Current		20.5			6.0			14.8
Deferred		(1.5	)		14.1			(0.9	)
Total state income taxes		19.0			20.1			13.9
Foreign income taxes:
Current		2.8			(1.4	)		1.2
Deferred		(0.5	)		2.1			0.5
Total foreign income taxes		2.3			0.7			1.7
Income tax expense (benefit)	$	136.3		$	105.7		$	(94.5	)

Summary of Effective Income Tax Rate

The Company’s effective income tax rate varied from the statutory United States income tax rate because of the following
tax differences:

years ended December 31	2019			2018			2017
Statutory income tax rate		21.0	%		21.0	%		35.0	%
(Reduction) increase resulting from:
Effect of statutory depletion		(3.4	)		(3.4	)		(5.6	)
State income taxes, net of federal tax benefit		2.0			2.8			1.5
Change in tax status of subsidiary		(1.7	)		—			—
Stock based compensation		(0.5	)		(0.5	)		(1.0	)
Impact from 2017 Tax Act		—			(3.3	)		(41.7	)
Domestic production deduction		—			—			(2.2	)
Other items		0.8			1.7			(1.3	)
Effective income tax rate		18.2	%		18.3	%		(15.3	%)

Components of Deferred Tax Assets and Liabilities

The principal components of the Company’s deferred tax assets and liabilities are as follows:

December 31	Deferred Assets (Liabilities)
(in millions)	2019			2018
Deferred tax assets related to:
Inventories	$	62.6		$	52.6
Valuation and other reserves		22.3			22.4
Net operating loss carryforwards		10.5			11.0
Accumulated other comprehensive loss		85.2			84.2
Lease liability		114.7			—
Other items, net		2.9			3.0
Gross deferred tax assets		298.2			173.2
Valuation allowance on deferred tax assets		(9.0	)		(8.6	)
Total net deferred tax assets		289.2			164.6
Deferred tax liabilities related to:
Property, plant and equipment		(700.8	)		(478.3	)
Goodwill and other intangibles		(151.7	)		(170.6	)
Right-of-use assets		(112.1	)		—
Partnerships and joint ventures		(27.4	)		(204.3	)
Employee benefits		(30.2	)		(17.0	)
Total deferred tax liabilities		(1,022.2	)		(870.2	)
Deferred income taxes, net	$	(733.0	)	$	(705.6	)

Schedule of Unrecognized Tax Benefits Excluding Interest Correlative Effects

The following table summarizes the Company’s unrecognized tax benefits, excluding interest and correlative effects of $1.7 million and $0.6 million for the years ended December 31, 2019 and 2018, respectively:

years ended December 31 (in millions)	2019			2018			2017
Unrecognized tax benefits at beginning of year	$	24.1		$	22.4		$	21.8
Gross increases – tax positions in prior years		0.4			0.9			1.4
Gross decreases – tax positions in prior years		—			—			(0.7	)
Gross increases – tax positions in current year		1.8			1.8			5.0
Gross decreases – tax positions in current year		(0.8	)		(1.0	)		(0.9	)
Lapse of statute of limitations		—			—			(4.2	)
Unrecognized tax benefits at end of year	$	25.5		$	24.1		$	22.4

Amount that, if recognized, would favorably impact the effective tax rate	$	15.5		$	12.8		$	10.4

Leases - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lessee Lease Description [Line Items]
Option to extend lease		options to extend the leases for up to 30 years
Option to terminate lease		options to terminate the leases within one year
Total royalties		$ 58.2	$ 52.5	$ 51.8
Lease expenses for operating lease			$ 122.5	$ 90.7
Subsequent Event
Lessee Lease Description [Line Items]
Lease term	15 years
Fixed rent payments for leases	$ 56.0
Minimum
Lessee Lease Description [Line Items]
Financing lease term		1 year
Estimated incremental percentage on interest rate		2.10%
Maximum
Lessee Lease Description [Line Items]
Financing lease term		53 years
Estimated incremental percentage on interest rate		5.50%

Business Combinations (Tables)

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

Summary of the Estimated Fair Values of the Assets Acquired and the Liabilities Assumed

The following is a summary of the estimated fair values of the assets acquired and the liabilities assumed as of the acquisition date:

(in millions)
Assets:
Cash and cash equivalents	$	1.2
Receivables		25.5
Inventory		46.6
Other current assets		1.0
Property, plant and equipment		1,519.3
Intangible assets, other than goodwill		20.2
Goodwill		243.0
Total Assets		1,856.8
Liabilities:
Accounts payable and accrued expenses		17.9
Deferred income tax liabilities, net		212.5
Noncontrolling interest		9.0
Total Liabilities		239.4
Total Consideration	$	1,617.4

Business Acquisition, Pro Forma Information

years ended December 31
(in millions, except for per share data)	2018		2017
Total revenues	$	4,299.7	$	4,178.6
Net earnings attributable to Martin Marietta	$	489.5	$	691.7
Diluted earnings per share	$	7.75	$	10.94

Leases - Summary of Balance Sheet Classifications of Operating and Finance Leases (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Operating Leases:
Operating lease right-of-use assets	$ 481.9
Current operating lease liabilities	52.7
Noncurrent operating lease liabilities	433.9
Total operating lease liabilities	486.6
Finance Leases:
Property, plant and equipment	18.3
Accumulated depreciation	(3.1)
Property, plant and equipment, net	15.2
Other current liabilities	2.8
Other noncurrent liabilities	5.9
Total finance lease liabilities	$ 8.7

Retirement Plans, Postretirement and Postemployment Benefits - Net Periodic Benefit Credit or Cost Not Yet Recognized (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit) - Gross	$ 6.4
Actuarial (gain) loss - Gross	229.4	$ 233.7
Total - Gross	235.8	233.7
Prior service cost (credit) - Net of tax	4.0
Actuarial (gain) loss - Net of tax	144.5	146.6
Total - Net of tax	148.5	146.6
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit) - Gross	(3.0)	(3.8)
Actuarial (gain) loss - Gross	(2.7)	(4.2)
Total - Gross	(5.7)	(8.0)
Prior service cost (credit) - Net of tax	(1.9)	(2.4)
Actuarial (gain) loss - Net of tax	(1.7)	(2.7)
Total - Net of tax	$ (3.6)	$ (5.1)

Stock-Based Compensation - Stock-Based Compensation Expense in Future for Outstanding Awards (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
2020	$ 14.9
2021	7.2
2022	0.8
2023	0.3
Total	$ 23.2

Stock-Based Compensation - Summary Information for Stock Options (Detail)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding at January 1, 2019 \| shares	210,390
Number of Options, Exercised \| shares	(150,722)
Number of Options, Terminated \| shares	(828)
Number of Options, Outstanding at December 31, 2019 \| shares	58,840
Number of Options, Exercisable at December 31, 2019 \| shares	58,840
Weighted-Average Exercise Price, Outstanding at January 1, 2019 \| $ / shares	$ 95.93
Weighted-Average Exercise Price, Exercised \| $ / shares	90.86
Weighted-Average Exercise Price, Terminated \| $ / shares	94.75
Weighted-Average Exercise Price, Outstanding at December 31, 2019 \| $ / shares	108.93
Weighted-Average Exercise Price, Exercisable at December 31, 2019 \| $ / shares	$ 108.93
Weighted-Average Remaining Contractual Life (years), Outstanding at December 31, 2019	3 years 1 month 6 days
Weighted-Average Remaining Contractual Life (years), Exercisable at December 31, 2019	3 years 1 month 6 days

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary Information for Restricted Stock Awards and Incentive Compensation Stock Awards

The following table summarizes information for restricted stock awards and incentive compensation stock awards for 2019:

	Restricted Stock - Service Based					Restricted Stock - Performance Based					Incentive Compensation Stock
	Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value		Number of Awards			Weighted- Average Grant-Date Fair Value
January 1, 2019		278,147		$	158.29		151,939		$	174.74		35,376		$	206.55
Awarded		86,922		$	196.91		49,644		$	192.27		21,883		$	192.27
Distributed		(171,689	)	$	148.72		(54,424	)	$	133.73		(15,948	)	$	206.23
Forfeited		(9,441	)	$	166.51		(5,329	)	$	205.21		(1,727	)	$	205.54
Adjustment for performance		—		$	—		(17,609	)	$	133.77		—		$	—
December 31, 2019		183,939		$	185.06		124,221		$	204.21		39,584		$	198.83

Summary Information for Stock Options

The following table includes summary information for stock options as of December 31, 2019:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (years)
Outstanding at January 1, 2019		210,390		$	95.93
Exercised		(150,722	)	$	90.86
Terminated		(828	)	$	94.75
Outstanding at December 31, 2019		58,840		$	108.93		3.1

Exercisable at December 31, 2019		58,840		$	108.93		3.1

Schedule of Stock-Based Compensation Expense

(in millions, except year data)	Stock Options		Restricted Stock		Incentive Compensation Stock		Directors’ Awards		Total
Stock-based compensation expense recognized for years ended December 31:
2019	$	0.1	$	32.6	$	0.8	$	0.6	$	34.1
2018	$	0.3	$	27.7	$	0.7	$	0.6	$	29.3
2017	$	0.7	$	28.7	$	0.7	$	0.4	$	30.5
Unrecognized compensation cost at December 31, 2019	$	—	$	22.7	$	0.5	$	—	$	23.2
Weighted-average period over which unrecognized compensation cost will be recognized			2.1 years		1.7 years

Stock-Based Compensation Expense in Future for Outstanding Awards

The following presents expected stock-based compensation expense in future periods for outstanding awards as of December 31, 2019:

(in millions)
2020	$	14.9
2021		7.2
2022		0.8
2023		0.3
Total	$	23.2

Document and Entity Information - USD ($)

12 Months Ended

Dec. 31, 2019

Feb. 14, 2020

Jun. 28, 2019

Cover [Abstract]

Document Type

10-K

Amendment Flag

false

Document Fiscal Year Focus

2019

Document Period End Date

Dec. 31, 2019

Document Annual Report

true

Document Transition Report

false

Entity File Number

1-12744

Entity Registrant Name

MARTIN MARIETTA MATERIALS, INC.

Document Fiscal Period Focus

Trading Symbol

MLM

Entity Central Index Key

0000916076

Entity Incorporation, State or Country Code

Entity Tax Identification Number

56-1848578

Entity Address, Address Line One

2710 Wycliff Road

Entity Address, City or Town

Raleigh

Entity Address, State or Province

Entity Address, Postal Zip Code

27607-3033

City Area Code

919

Local Phone Number

781-4550

Title of 12(b) Security

Common Stock (par value $.01 per share)

Security Exchange Name

NYSE

Entity Well-known Seasoned Issuer

Yes

Entity Voluntary Filers

Entity Current Reporting Status

Yes

Entity Interactive Data Current

Yes

Entity Filer Category

Large Accelerated Filer

Entity Shell Company

false

Entity Common Stock, Shares Outstanding

62,198,867

Entity Public Float

$ 12,807,658,433.72

Entity Emerging Growth Company

false

Entity Small Business

false

Current Fiscal Year End Date

--12-31

Documents Incorporated by Reference

DOCUMENTS INCORPORATED BY REFERENCE

Document		Parts Into Which Incorporated
Proxy Statement for the Annual Meeting of Shareholders to be held May 14, 2020 (Proxy Statement)		Part III

Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Estimated Service Lives for Property Plant and Equipment

The estimated service lives for property, plant and equipment are as follows:

Class of Assets		Range of Service Lives
Buildings		5 to 20 years
Machinery & Equipment		2 to 20 years
Land Improvements		5 to 60 years

Components of Changes in Accumulated Other Comprehensive Loss and Related Cumulative Noncurrent Deferred Tax Assets

The components of the changes in accumulated other comprehensive loss and related cumulative noncurrent deferred tax assets are as follows:

	Pension and Postretirement Benefit Plans			Foreign Currency			Unamortized Value of Terminated Forward Starting Interest Rate Swap			Total
years ended December 31 (in millions)	2019
Accumulated other comprehensive loss at beginning of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Other comprehensive (loss) earnings before reclassifications, net of tax		(14.5	)		1.2			—			(13.3	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		11.1			—			—			11.1
Other comprehensive (loss) earnings, net of tax		(3.4	)		1.2			—			(2.2	)
Accumulated other comprehensive loss at end of period	$	(144.9	)	$	(0.9	)	$	—		$	(145.8	)
Cumulative noncurrent deferred tax assets at end of period	$	85.2		$	—		$	—		$	85.2

	2018
Accumulated other comprehensive loss at beginning of period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Other comprehensive loss before reclassifications, net of tax		(22.9	)		(2.1	)		—			(25.0	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		10.2			—			0.3			10.5
Other comprehensive (loss) earnings, net of tax		(12.7	)		(2.1	)		0.3			(14.5	)
Accumulated other comprehensive loss at end of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Cumulative noncurrent deferred tax assets at end of period	$	84.2		$	—		$	—		$	84.2

	2017
Accumulated other comprehensive loss at beginning of period	$	(128.4	)	$	(1.2	)	$	(1.1	)	$	(130.7	)
Other comprehensive (loss) earnings before reclassifications, net of tax		(8.1	)		1.2			—			(6.9	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		7.7			—			0.8			8.5
Other comprehensive (loss) earnings, net of tax		(0.4	)		1.2			0.8			1.6
Accumulated other comprehensive loss at end of period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Cumulative noncurrent deferred tax assets at end of period	$	79.9		$	—		$	0.2		$	80.1

Reclassification Out of Accumulated Other Comprehensive Loss

Reclassifications out of accumulated other comprehensive loss are as follows:

years ended December 31 (in millions)	2019			2018			2017			Affected line items in the consolidated statements of earnings
Pension and postretirement benefit plans:
Settlement charge	$	—		$	2.9		$	—
Amortization of:
Prior service credit		(0.8	)		(2.0	)		(1.4	)
Actuarial loss		15.5			12.7			13.8
		14.7			13.6			12.4		Other nonoperating expenses and (income), net
Tax effect		(3.6	)		(3.4	)		(4.7	)	Income tax expense (benefit)
Total	$	11.1		$	10.2		$	7.7
Unamortized value of terminated forward starting interest rate swap:
Additional interest expense	$	—		$	0.5		$	1.4		Interest expense
Tax effect		—			(0.2	)		(0.6	)	Income tax expense (benefit)
Total	$	—		$	0.3		$	0.8

Basic and Diluted Earnings Per Common Share

The following table reconciles the numerator and denominator for basic and diluted earnings per common share:

years ended December 31 (in millions)	2019		2018		2017
Net earnings attributable to Martin Marietta	$	611.9	$	470.0	$	713.3
Less: Distributed and undistributed earnings attributable to unvested participating securities		0.9		0.8		2.0
Basic and diluted net earnings attributable to common shareholders attributable to Martin Marietta	$	611.0	$	469.2	$	711.3

Basic weighted-average common shares outstanding		62.5		62.9		62.9
Effect of dilutive employee and director awards		0.2		0.2		0.3
Diluted weighted-average common shares outstanding		62.7		63.1		63.2

Retirement Plans, Postretirement and Postemployment Benefits

12 Months Ended

Dec. 31, 2019

Compensation And Retirement Disclosure [Abstract]

Retirement Plans, Postretirement and Postemployment Benefits

Note K: Retirement Plans, Postretirement and Postemployment Benefits

The Company sponsors defined benefit retirement plans that cover substantially all employees. Additionally, the Company provides other postretirement benefits for certain employees, including medical benefits for retirees and their spouses and retiree life insurance. Employees starting on or after January 1, 2002 are not eligible for postretirement welfare plans. The Company also provides certain benefits, such as disability benefits, to former or inactive employees after employment but before retirement.

The measurement date for the Company’s defined benefit plans, postretirement benefit plans and postemployment benefit plans is December 31.

Defined Benefit Retirement Plans. Retirement plan assets are invested in listed stocks, bonds, hedge funds, real estate and cash equivalents. Defined retirement benefits for salaried employees are based on each employee’s years of service and average compensation for a specified period of time before retirement. Defined retirement benefits for hourly employees are generally stated amounts for specified periods of service.

The Company sponsors a Supplemental Excess Retirement Plan (SERP) that generally provides for the payment of retirement benefits in excess of allowable Internal Revenue Code limits. The SERP generally provides for a lump-sum payment of vested benefits. When these benefit payments exceed the sum of the service and interest costs for the SERP during a year, the Company recognizes a pro rata portion of the SERP’s unrecognized actuarial loss as settlement expense.

The net periodic retirement benefit cost of defined benefit plans includes the following components:

years ended December 31 (in millions)	2019			2018			2017
Service cost	$	30.8		$	31.7		$	26.9
Interest cost		37.6			33.2			36.1
Expected return on assets		(47.9	)		(46.0	)		(39.8	)
Amortization of:
Prior service cost		—			0.1			0.3
Actuarial loss		16.0			12.8			14.1
Settlement charge		—			2.9			—
Net periodic benefit cost	$	36.5		$	34.7		$	37.6

The components of net periodic benefit cost, other than service cost, are included in the line item Other nonoperating expenses and (income), net, in the consolidated statements of earnings.

The expected return on assets is calculated by applying an annually selected expected rate of return assumption to the estimated fair value of the plan assets, giving consideration to contributions and benefits paid.

The Company recognized the following amounts in consolidated comprehensive earnings:

years ended December 31
(in millions)	2019			2018			2017
Actuarial loss	$	11.7		$	32.1		$	13.3
Net prior service cost		6.4			—			—
Amortization of:
Prior service cost		—			(0.1	)		(0.3	)
Actuarial loss		(16.0	)		(12.8	)		(14.1	)
Settlement charge		—			(2.9	)		—
Total	$	2.1		$	16.3		$	(1.1	)

Accumulated other comprehensive loss includes the following amounts that have not yet been recognized in net periodic benefit cost:

December 31	2019				2018
(in millions)	Gross		Net of tax		Gross		Net of tax
Prior service cost	$	6.4	$	4.0	$	—	$	—
Actuarial loss		229.4		144.5		233.7		146.6
Total	$	235.8	$	148.5	$	233.7	$	146.6

The prior service cost and actuarial loss expected to be recognized in net periodic benefit cost during 2020 are $0.7 million (net of deferred taxes of $0.2 million) and $13.5 million (net of deferred taxes of $3.3 million), respectively. These amounts are included in accumulated other comprehensive loss at December 31, 2019.

The defined benefit plans’ change in projected benefit obligation is as follows:

years ended December 31
(in millions)	2019			2018
Net projected benefit obligation at beginning of year	$	847.9		$	879.3
Service cost		30.8			31.7
Interest cost		37.6			33.2
Actuarial loss (gain)		95.2			(54.6	)
Plan amendments		6.4			—
Gross benefits paid		(40.1	)		(41.7	)
Net projected benefit obligation at end of year	$	977.8		$	847.9

The Company’s change in plan assets, funded status and amounts recognized on the Company’s consolidated balance sheets are as follows:

years ended December 31
(in millions)	2019			2018
Fair value of plan assets at beginning of year	$	717.9		$	638.1
Actual return on plan assets, net		131.3			(40.8	)
Employer contributions		58.9			162.3
Gross benefits paid		(40.1	)		(41.7	)
Fair value of plan assets at end of year	$	868.0		$	717.9

December 31
(in millions)	2019			2018
Funded status of the plan at end of year	$	(109.8	)	$	(130.0	)
Accrued benefit cost	$	(109.8	)	$	(130.0	)

December 31
(in millions)	2019			2018
Amounts recognized on consolidated balance sheets consist of:
Current liability	$	(6.4	)	$	(9.0	)
Noncurrent liability		(103.4	)		(121.0	)
Net amount recognized at end of year	$	(109.8	)	$	(130.0	)

The accumulated benefit obligation for all defined benefit pension plans was $878.7 million and $771.9 million at December 31, 2019 and 2018, respectively.

Benefit obligations and fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets are as follows:

December 31
(in millions)	2019		2018
Projected benefit obligation	$	107.1	$	98.7
Accumulated benefit obligation	$	96.4	$	85.5
Fair value of plan assets	$	0.6	$	0.6

Weighted-average assumptions used to determine benefit obligations as of December 31 are:

	2019	2018
Discount rate	3.69%	4.38%
Rate of increase in future compensation levels	4.50%	4.50%

Weighted-average assumptions used to determine net periodic benefit cost for the years ended December 31 are:

	2019	2018	2017
Discount rate	4.38%	3.76%	4.29%
Rate of increase in future compensation levels	4.50%	4.50%	4.50%
Expected long-term rate of return on assets	6.75%	6.75%	6.75%

The expected long-term rate of return on assets is based on a building-block approach, whereby the components are weighted based on the allocation of pension plan assets.

As of December 31, 2019 and 2018, the Company estimated the remaining lives of participants in the pension plans using the Pri-2012 and RP-2014 Base tables, respectively. The no-collar table was used for salaried participants and the blue-collar table was used for hourly participants; both tables were adjusted to reflect the experience of the Company’s participants. The Company used the MP-2018 mortality improvement scale for the years 2019 and 2018.

The target allocation for 2019 and the actual pension plan asset allocation by asset class are as follows:

	Percentage of Plan Assets
		2019
		Target	December 31
Asset Class		Allocation	2019	2018
Equity securities		56%	64%	57%
Debt securities		30%	28%	32%
Hedge funds		4%	3%	6%
Real estate		10%	5%	5%
Total		100%	100%	100%

The Company’s investment strategy is for approximately 45% of equity securities, excluding hedge funds and real estate, to be invested in mid-sized to large capitalization U.S. funds, with the remaining invested in small capitalization, emerging markets and international funds. Debt securities, or fixed income investments, are invested in funds benchmarked to the Barclays U.S. Aggregate Bond Index.

The fair values of pension plan assets by asset class and fair value hierarchy level are as follows:

	Fair Value Measurements
December 31		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Net Asset Value		Total Fair Value
(in millions)		2019
Equity securities¹:
Mid-sized to large cap		$	—	$	—	$	—	$	262.5	$	262.5
Small cap, international and emerging growth funds			—		—		—		290.3		290.3
Debt securities¹:
Core fixed income			—		—		—		242.9		242.9
Real estate			—		—		—		42.9		42.9
Hedge funds			—		—		—		26.4		26.4
Cash equivalents			3.0		—		—		—		3.0
Total		$	3.0	$	—	$	—	$	865.0	$	868.0

		2018
Equity securities¹:
Mid-sized to large cap		$	—	$	—	$	—	$	196.5	$	196.5
Small cap, international and emerging growth funds			—		—		—		210.4		210.4
Debt securities¹:
Core fixed income			—		—		—		228.2		228.2
Real estate			—		—		—		35.5		35.5
Hedge funds			—		—		—		44.4		44.4
Cash equivalents			2.9		—		—		—		2.9
Total		$	2.9	$	—	$	—	$	715.0	$	717.9

¹	These investments are common collective investment trusts valued using the net asset value (NAV) unit price provided by the fund administrator. The NAV is based on the value of the underlying assets owned by the fund.

Real estate investments are stated at estimated fair value, which is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair values of real estate investments generally do not reflect transaction costs that may be incurred upon disposition of the real estate investments and do not necessarily represent the prices at which the real estate investments would be sold or repaid, since market prices of real estate investments can only be determined by negotiation between a willing buyer and seller. An independent valuation consultant is employed to determine the fair value of the real estate investments. The value of hedge funds is based on the values of the sub-fund investments. In determining the fair value of each sub-fund’s investment, the hedge funds’ Board of Trustees uses the values provided by the sub-funds and any other considerations that may, in its judgment, increase or decrease such estimated value.

In 2019 and 2018, the Company made combined pension plan and SERP contributions of $58.9 million and $162.3 million, respectively. The Company currently estimates that it will contribute $60.2 million to its pension plans in 2020.

The expected benefit payments to be paid from plan assets for each of the next five years and the five-year period thereafter are as follows:

(in millions)
2020	$	43.5
2021	$	44.8
2022	$	46.2
2023	$	47.6
2024	$	50.9
Years 2025 - 2029	$	271.0

Postretirement Benefits. The net periodic postretirement benefit credit for postretirement plans includes the following components:

years ended December 31
(in millions)	2019			2018			2017
Service cost	$	0.1		$	0.1		$	0.1
Interest cost		0.6			0.5			0.7
Amortization of:
Prior service credit		(0.8	)		(2.1	)		(1.7	)
Actuarial gain		(0.5	)		(0.2	)		(0.4	)
Total net periodic benefit credit	$	(0.6	)	$	(1.7	)	$	(1.3	)

The components of net periodic benefit credit, other than service cost, are included in the line item Other nonoperating expenses and (income), net, in the consolidated statements of earnings.

The Company recognized the following amounts in consolidated comprehensive earnings:

years ended December 31
(in millions)	2019		2018			2017
Actuarial loss (gain)	$	1.0	$	(1.7	)	$	1.2
Net prior service credit		—		—			(3.9	)
Amortization of:
Prior service credit		0.8		2.1			1.7
Actuarial gain		0.5		0.2			0.4
Total	$	2.3	$	0.6		$	(0.6	)

Accumulated other comprehensive loss includes the following amounts that have not yet been recognized in net periodic benefit credit:

December 31	2019						2018
(in millions)	Gross			Net of tax			Gross			Net of tax
Prior service credit	$	(3.0	)	$	(1.9	)	$	(3.8	)	$	(2.4	)
Actuarial gain		(2.7	)		(1.7	)		(4.2	)		(2.7	)
Total	$	(5.7	)	$	(3.6	)	$	(8.0	)	$	(5.1	)

The prior service credit and actuarial gain expected to be recognized in net periodic benefit cost during 2020 are $0.8 million (net of deferred taxes of $0.2 million) and $0.3 million (net of deferred taxes of $0.1 million), respectively, and are included in accumulated other comprehensive loss at December 31, 2019.

The postretirement health care plans’ change in benefit obligation is as follows:

years ended December 31
(in millions)	2019			2018
Net benefit obligation at beginning of year	$	13.3		$	15.3
Service cost		0.1			0.1
Interest cost		0.6			0.5
Participants’ contributions		1.2			0.3
Actuarial loss (gain)		1.0			(1.6	)
Gross benefits paid		(3.2	)		(1.3	)
Net benefit obligation at end of year	$	13.0		$	13.3

The postretirement health care plans’ change in plan assets, funded status and amounts recognized on the Company’s consolidated balance sheets are as follows:

years ended December 31
(in millions)	2019			2018
Fair value of plan assets at beginning of year	$	—		$	—
Employer contributions		2.0			1.0
Participants’ contributions		1.2			0.3
Gross benefits paid		(3.2	)		(1.3	)
Fair value of plan assets at end of year	$	—		$	—

December 31
(in millions)	2019			2018
Funded status of the plan at end of year	$	(13.0	)	$	(13.3	)
Accrued benefit cost	$	(13.0	)	$	(13.3	)

December 31
(in millions)	2019			2018
Amounts recognized on consolidated balance sheets consist of:
Current liability	$	(2.0	)	$	(1.0	)
Noncurrent liability		(11.0	)		(12.3	)
Net amount recognized at end of year	$	(13.0	)	$	(13.3	)

Weighted-average assumptions used to determine the postretirement benefit obligation as of December 31 are:

		2019			2018
Discount rate		3.29%			4.15%

Weighted-average assumptions used to determine net postretirement benefit credit for the years ended December 31 are:

		2019			2018			2017
Discount rate		4.15%			3.47%			3.78%

As of December 31, 2019 and 2018, the Company estimated the remaining lives of participants in the postretirement benefit plans using the Pri-2012 and RP-2014 Base tables, respectively. The no-collar table was used for salaried participants and the blue-collar table was used for hourly participants; both tables were adjusted to reflect the experience of the Company’s participants. The Company used the MP-2018 mortality improvement scale for the years 2019 and 2018.

Assumed health care cost trend rates at December 31 are:

	2019	2018
Health care cost trend rate assumed for next year	6.75%	7.0%
Rate to which the cost trend rate gradually declines	4.75%	5.0%
Year the rate reaches the ultimate rate	2028	2023

Assumed health care cost trend rates have a significant effect on the amounts reported for the Company’s health care plans. A one percentage-point change in assumed health care cost trend rates would have the following effects:

	One Percentage Point
(in millions)	Increase		(Decrease)
Total service and interest cost components	$	—	$	—
Postretirement benefit obligation	$	0.7	$	(0.6	)

The Company estimates that it will contribute $2.0 million to its postretirement health care plans in 2020.

The total expected benefit payments to be paid by the Company, net of participant contributions, for each of the next five years and the five-year period thereafter are as follows:

(in millions)
2020	$	2.0
2021	$	1.4
2022	$	1.4
2023	$	1.3
2024	$	1.2
Years 2025 - 2029	$	4.7

Defined Contribution Plan. The Company maintains a defined contribution plan that covers substantially all employees. This plan, qualified under Section 401(a) of the Internal Revenue Code, is a retirement savings and investment plan for the Company’s salaried and hourly employees. Under certain provisions of the plan, the Company, at established rates, matches employees’ eligible contributions. The Company’s matching obligations were $17.6 million in 2019, $16.5 million in 2018 and $14.9 million in 2017.

Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Allowance for doubtful accounts

Valuation And Qualifying Accounts Disclosure [Line Items]

Balance at beginning of period

$ 3.3

$ 2.4

$ 6.3

Charged to costs and expenses

1.4

0.9

Deductions-describe

^[1]

3.9

Balance at end of period

4.7

3.3

2.4

Allowance for uncollectible notes receivable

Valuation And Qualifying Accounts Disclosure [Line Items]

Balance at beginning of period

0.2

0.4

Deductions-describe

^[1]

0.2

Balance at end of period

0.2

Inventory valuation allowance

Valuation And Qualifying Accounts Disclosure [Line Items]

Balance at beginning of period

159.2

144.0

134.9

Charged to costs and expenses

38.8

36.9

38.5

Charged to other accounts-describe

^[2]

5.1

Deductions-describe

^[3]

29.4

26.8

29.4

Balance at end of period

$ 168.6

$ 159.2

$ 144.0

[1]	Write-off of uncollectible accounts and change in estimates
[2]	Application of reserve policy to acquired inventories
[3]	Sale of reserved inventory and divestitures

Income Taxes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Federal statutory corporate income tax rate		21.00%	21.00%	35.00%
Tax benefit for the provisional impact of 2017 Tax Act				$ 258.1
Income tax benefit from net operating loss (NOL) carryforwards utilized			$ 5.8
Foreign pretax earnings		$ 15.1	5.7	10.6
Increased net earnings		$ 15.2		$ 15.5
Increased net earnings, per share		$ 0.24		$ 0.25
Tax deduction, percentage				9.00%
Operating loss carryforwards, expiration dates		2039
Deferred tax assets recognized		$ 10.5	11.0
Deferred tax asset, valuation allowance		$ 9.0	8.6
Percentage of impact of expensing of capital expenditures for tax purposes and change in tax status		100.00%
Unrecognized tax benefits, excluding interest and correlative effects		$ 1.7	0.6
Tax refund				$ 3.9
Open tax years		2011 2012 2013 2014 2015 2016 2017 2018 2019
Maximum \| Scenario, Forecast
Income Taxes [Line Items]
Decrease in unrecognized tax benefits, excluding interest and correlative effects	$ 17.1
Federal Tax Authority
Income Taxes [Line Items]
Operating loss carryforwards, amount		$ 4.1	3.2
State Tax Authority
Income Taxes [Line Items]
Operating loss carryforwards, amount		161.0	168.1
Domestic State Tax Authority
Income Taxes [Line Items]
Domestic and foreign tax credits, amount		$ 1.1	1.0
Domestic tax credits, expiration year		2039
Deferred tax assets recognized		$ 0.9	0.8
Tax Year 2017
Income Taxes [Line Items]
Income tax expense for transition tax on undistributed foreign earnings			1.1
Income tax expense, write off of deferred tax assets			1.5
Income tax benefit of pension funding, inventory and insurance prepayments			$ 21.5
Earliest Tax Year
Income Taxes [Line Items]
Expiration date of statute of limitations		2010
Latest Tax Year
Income Taxes [Line Items]
Expiration date of statute of limitations		2013

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 34.1	$ 29.3	$ 30.5
Unrecognized compensation cost	23.2
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	0.1	0.3	0.7
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	32.6	27.7	28.7
Unrecognized compensation cost	$ 22.7
Weighted-average period over which unrecognized compensation cost will be recognized	2 years 1 month 6 days
Incentive Compensation Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 0.8	0.7	0.7
Unrecognized compensation cost	$ 0.5
Weighted-average period over which unrecognized compensation cost will be recognized	1 year 8 months 12 days
Directors' Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 0.6	$ 0.6	$ 0.4

Revenues and Gross Profit - Domestic and Foreign Total Revenues (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Consolidated total revenues	$ 4,739.1	$ 4,244.3	$ 3,965.6
Domestic
Segment Reporting Information [Line Items]
Consolidated total revenues	4,676.3	4,166.4	3,901.3
Foreign
Segment Reporting Information [Line Items]
Consolidated total revenues	$ 62.8	$ 77.9	$ 64.3

Consolidated Statements of Comprehensive Earnings - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Consolidated Net Earnings	$ 612.0	$ 470.4	$ 713.4
Defined benefit pension and postretirement plans:
Net loss arising during period, net of tax of $(4.8), $(7.6) and $(2.6), respectively	(14.5)	(22.9)	(8.1)
Amortization of prior service credit, net of tax of $(0.2), $(0.5) and $(0.5), respectively	(0.6)	(1.5)	(0.8)
Amortization of actuarial loss, net of tax of $3.8, $3.2 and $5.3, respectively	11.7	9.5	8.5
Amount recognized in net periodic pension cost due to settlement, net of tax of $0.0, $0.7 and $0.0 respectively		2.2
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(3.4)	(12.7)	(0.4)
Foreign currency translation gain (loss)	1.2	(2.1)	1.2
Amortization of terminated value of forward starting interest rate swap agreements into interest expense, net of tax of $0.0, $0.2 and $0.6, respectively		0.3	0.8
Other Comprehensive Income (Loss), Net of Tax	(2.2)	(14.5)	1.6
Consolidated comprehensive earnings	609.8	455.9	715.0
Less: Comprehensive earnings attributable to noncontrolling interests	0.1	0.4	0.1
Comprehensive Earnings Attributable to Martin Marietta	$ 609.7	$ 455.5	$ 714.9

Other Operating (Income) and Expenses, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Component Of Other Operating Income And Expense [Line Items]
Other operating expenses and (income), net	$ 9.1	$ 18.2	$ (0.8)
Asset and portfolio rationalization charge		18.8
Gain (Loss) Related to Litigation Settlement		7.7
Gain (Loss) on Sale of Properties		25.3
Gain on sale of assets, excess land	3.1	39.3	19.4
Nonrecurring repair costs			12.7
Reversal of accruals for sales tax and unclaimed property contingencies	6.9
Noncash portion of asset and portfolio rationalization charge	17.0	$ 17.0
Cash portion of asset and portfolio rationalization charge	$ 1.8
Other Operating (Income) and Expenses, Net
Component Of Other Operating Income And Expense [Line Items]
Gain on sale of assets, excess land			19.4
Other Operating (Income) and Expenses, Net \| Executive
Component Of Other Operating Income And Expense [Line Items]
Retirement expense			$ 10.8

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities:
Consolidated net earnings	$ 612.0	$ 470.4	$ 713.4
Adjustments to reconcile consolidated net earnings to net cash provided by operating activities:
Depreciation, depletion and amortization	371.5	344.0	297.2
Stock-based compensation expense	34.1	29.3	30.5
Gains on divestitures and sales of assets	(3.1)	(39.3)	(19.4)
Deferred income taxes, net	29.4	85.1	(239.1)
Noncash portion of asset and portfolio rationalization charge	17.0	17.0
Other items, net	8.6	(9.0)	(13.4)
Changes in operating assets and liabilities, net of effects of acquisitions and divestitures:
Accounts receivable, net	(50.4)	(10.6)	(29.3)
Inventories, net	(27.7)	(22.0)	(79.0)
Accounts payable	25.9	20.1	(17.9)
Other assets and liabilities, net	(34.2)	(179.9)	14.6
Net Cash Provided by Operating Activities	966.1	705.1	657.6
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(393.5)	(376.0)	(410.3)
Acquisitions, net of cash acquired		(1,642.1)	(12.1)
Proceeds from divestitures and sales of assets	8.4	69.1	36.0
Payment of railcar construction advances		(79.4)	(43.6)
Reimbursement of railcar construction advances		79.4	43.6
Investments in life insurance contracts, net	0.6	0.8	0.3
Other investing activities, net	(1.4)
Net Cash Used for Investing Activities	(385.9)	(1,948.2)	(386.1)
Cash Flows from Financing Activities:
Borrowings of long-term debt	625.0	1,000.0	2,408.8
Repayments of long-term debt	(975.1)	(910.1)	(1,065.0)
Debt issuance costs		(3.9)	(2.2)
Payments on finance lease obligations	(11.0)
Payments on capital lease obligations		(3.5)	(3.5)
Dividends paid	(129.8)	(116.4)	(108.9)
Repurchases of common stock	(98.2)	(100.4)	(100.0)
Payments of deferred acquisition consideration		(6.7)	(2.8)
Purchase of the noncontrolling interest in the existing joint venture		(12.8)
Distributions to owners of noncontrolling interest	(0.6)
Contributions by noncontrolling interest to joint venture			0.2
Proceeds from exercise of stock options	13.7	7.3	10.1
Shares withheld for employees’ income tax obligations	(28.1)	(11.9)	(11.8)
Net Cash (Used for) Provided by Financing Activities	(604.1)	(158.4)	1,124.9
Net (Decrease) Increase in Cash and Cash Equivalents	(23.9)	(1,401.5)	1,396.4
Cash and Cash Equivalents, beginning of year	44.9	1,446.4	50.0
Cash and Cash Equivalents, end of year	$ 21.0	$ 44.9	$ 1,446.4

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Long-Term Debt

December 31 (in millions)	2019			2018
4.25% Senior Notes, due 2024	$	397.0		$	396.4
7% Debentures, due 2025		124.4			124.3
3.450% Senior Notes, due 2027		297.3			296.9
3.500% Senior Notes, due 2027		495.3			494.8
6.25% Senior Notes, due 2037		228.1			228.1
4.250% Senior Notes, due 2047		591.7			591.5
Floating Rate Senior Notes, due 2020, interest rate of 2.55% and 3.30% at December 31, 2019 and 2018, respectively		299.7			299.0
Floating Rate Senior Notes, due 2019, interest rate of 3.29% at December 31, 2018		—			299.2
Trade Receivable Facility, interest rate of 2.42% and 3.07% at December 31, 2019 and 2018, respectively		340.0			390.0
Other notes		0.1			0.2
Total		2,773.6			3,120.4
Less: current maturities		(340.0	)		(390.0	)
Long-term debt	$	2,433.6		$	2,730.4

Schedule of Principal Amount, Effective Interest Rate and Maturity Date for Corporation's Senior Notes

	Principal Amount (in millions)		Effective Interest Rate	Maturity Date
4.25% Senior Notes	$	400.0	4.25%	July 2, 2024
7% Debentures	$	125.0	7.12%	December 1, 2025
3.450% Senior Notes	$	300.0	3.47%	June 1, 2027
3.500% Senior Notes	$	500.0	3.53%	December 15, 2027
6.25% Senior Notes	$	230.0	6.45%	May 1, 2037
4.250% Senior Notes	$	600.0	4.27%	December 15, 2047
Floating Rate Senior Notes, due 2020	$	300.0	Three-month LIBOR + 0.65%	May 22, 2020

Schedule of Corporation's Long-Term Debt Maturities

The Company’s long-term debt maturities for the five years following December 31, 2019, and thereafter are:

(in millions)
2020	$	340.0
2021		0.1
2022		0.1
2023		—
2024		696.7
Thereafter		1,736.7
Total	$	2,773.6

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Segments

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

Segments

Note P: Segments

The Building Materials business is comprised of divisions which represent operating segments, some of which are consolidated into reportable segments for financial reporting purposes as they meet the aggregation criteria. The Building Materials business contains three reportable segments: Mid-America Group, Southeast Group and West Group. The

Magnesia Specialties business represents an individual operating and reportable segment. The accounting policies used for segment reporting are the same as those described in Note A.

The Chief Operating Decision Maker’s evaluation of performance and allocation of resources are based primarily on earnings from operations. Consolidated earnings from operations include total revenues less cost of revenues; selling, general and administrative expenses; acquisition-related expenses, net; other operating income and expenses, net; and exclude interest expense; other nonoperating income and expenses, net; and income tax expense (benefit). Corporate loss from operations primarily includes depreciation on capitalized interest; expenses for corporate administrative functions; acquisition-related expenses, net; and other nonrecurring and/or non-operational income and expenses excluded from the Company’s evaluation of segment performance and resource allocation. All long-term debt and related interest expense are held at Corporate.

Assets employed by segment include assets directly identified with those operations. Corporate assets consist primarily of cash and cash equivalents; property, plant and equipment for corporate operations; investments and other assets not directly identifiable with a reportable segment.

years ended December 31 (in millions) Total revenues	2019		2018		2017
Mid-America Group	$	1,446.0	$	1,223.2	$	1,053.3
Southeast Group		506.4		423.4		362.6
West Group		2,515.4		2,310.0		2,279.7
Total Building Materials Business		4,467.8		3,956.6		3,695.6
Magnesia Specialties		271.3		287.7		270.0
Total	$	4,739.1	$	4,244.3	$	3,965.6

Gross profit
Mid-America Group	$	482.9	$	366.9	$	335.4
Southeast Group		124.1		77.2		74.6
West Group		473.6		416.2		465.6
Total Building Materials Business		1,080.6		860.3		875.6
Magnesia Specialties		95.4		98.7		89.4
Corporate		3.0		7.6		6.9
Total	$	1,179.0	$	966.6	$	971.9

Selling, general and administrative expenses
Mid-America Group	$	63.1	$	55.8	$	53.9
Southeast Group		21.6		18.7		17.1
West Group		116.3		107.6		102.7
Total Building Materials Business		201.0		182.1		173.7
Magnesia Specialties		11.3		10.0		9.5
Corporate		90.4		88.5		78.9
Total	$	302.7	$	280.6	$	262.1

years ended December 31 (in millions) Earnings (Loss) from operations	2019			2018			2017
Mid-America Group	$	425.9		$	319.1		$	284.8
Southeast Group		103.1			75.9			61.2
West Group		365.2			295.8			360.6
Total Building Materials Business		894.2			690.8			706.6
Magnesia Specialties		83.6			88.1			79.4
Corporate		(92.9	)		(88.2	)		(85.6	)
Total	$	884.9		$	690.7		$	700.4

Earnings from operations for the West Group for 2018 reflect an asset and portfolio rationalization charge of $18.8 million.

December 31 (in millions) Assets employed	2019		2018		2017
Mid-America Group	$	2,879.3	$	2,788.5	$	1,532.9
Southeast Group		1,442.5		1,299.5		616.3
West Group		5,320.7		4,989.6		5,014.2
Total Building Materials Business		9,642.5		9,077.6		7,163.4
Magnesia Specialties		176.2		156.1		152.3
Corporate		312.9		317.7		1,676.8
Total	$	10,131.6	$	9,551.4	$	8,992.5

years ended December 31 (in millions) Depreciation, depletion and amortization	2019		2018		2017
Mid-America Group	$	110.2	$	93.6	$	69.7
Southeast Group		47.8		41.2		30.8
West Group		183.3		180.9		169.8
Total Building Materials Business		341.3		315.7		270.3
Magnesia Specialties		10.2		10.4		10.1
Corporate		20.0		17.9		16.8
Total	$	371.5	$	344.0	$	297.2

Total property additions, including the impact of acquisitions
Mid-America Group	$	127.7	$	1,157.1	$	139.5
Southeast Group		45.3		603.1		34.6
West Group		182.6		148.1		240.8
Total Building Materials Business		355.6		1,908.3		414.9
Magnesia Specialties		20.0		12.5		11.1
Corporate		12.0		4.8		12.6
Total	$	387.6	$	1,925.6	$	438.6

years ended December 31 (in millions) Property additions through acquisitions	2019		2018		2017
Mid-America Group	$	—	$	980.3	$	0.1
Southeast Group		—		561.5		—
West Group		—		1.4		2.4
Total Building Materials Business		—		1,543.2		2.5
Magnesia Specialties		—		—		—
Corporate		—		—		—
Total	$	—	$	1,543.2	$	2.5

Goodwill and Other Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Changes in Goodwill

The following table shows the changes in goodwill by reportable segment and in total:

December 31	Mid- America Group			Southeast Group			West Group			Total
(in millions)	2019
Balance at beginning of period	$	431.9		$	144.2		$	1,823.0		$	2,399.1
Measurement period adjustments		(1.0	)		(0.6	)		—			(1.6	)
Goodwill allocated to assets held for sale		—			(0.2	)		—			(0.2	)
Divestitures		—			—			(0.5	)		(0.5	)
Balance at end of period	$	430.9		$	143.4		$	1,822.5		$	2,396.8

	2018
Balance at beginning of period	$	281.4		$	50.3		$	1,828.6		$	2,160.3
Acquisitions		150.5			94.8			—			245.3
Goodwill allocated to assets held for sale		—			—			(5.6	)		(5.6	)
Divestitures		—			(0.9	)		—			(0.9	)
Balance at end of period	$	431.9		$	144.2		$	1,823.0		$	2,399.1

Intangible Assets Subject to Amortization

Intangible assets subject to amortization consist of the following:

December 31	Gross Amount		Accumulated Amortization			Net Balance
(in millions)	2019
Noncompetition agreements	$	6.3	$	(6.2	)	$	0.1
Customer relationships		65.6		(30.4	)		35.2
Operating permits		459.0		(42.3	)		416.7
Use rights and other		16.7		(12.1	)		4.6
Trade names		12.8		(10.9	)		1.9
Total	$	560.4	$	(101.9	)	$	458.5

	2018
Noncompetition agreements	$	6.3	$	(6.2	)	$	0.1
Customer relationships		65.6		(25.6	)		40.0
Operating permits		459.0		(36.1	)		422.9
Use rights and other		16.7		(11.2	)		5.5
Trade names		12.8		(9.7	)		3.1
Total	$	560.4	$	(88.8	)	$	471.6

Intangible Assets Deemed to Indefinite Life that are Therefore Not Amortized

Intangible assets deemed to have an indefinite life that are therefore not amortized consist of the following:

December 31	Building Materials Business		Magnesia Specialties		Total
(in millions)	2019
Operating permits	$	6.6	$	—	$	6.6
Use rights		19.0		—		19.0
Trade names		0.2		2.5		2.7
Total	$	25.8	$	2.5	$	28.3

	2018
Operating permits	$	6.6	$	—	$	6.6
Use rights		20.3		—		20.3
Trade names		0.3		2.5		2.8
Total	$	27.2	$	2.5	$	29.7

Estimated Amortization Expense of Intangible Assets

The estimated amortization expense for intangible assets for each of the next five years and thereafter is as follows:

(in millions)
2020	$	13.2
2021		12.5
2022		11.1
2023		10.6
2024		10.6
Thereafter		400.5
Total	$	458.5

Long-Term Debt

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Long-Term Debt

Note H: Long-Term Debt

December 31 (in millions)	2019			2018
4.25% Senior Notes, due 2024	$	397.0		$	396.4
7% Debentures, due 2025		124.4			124.3
3.450% Senior Notes, due 2027		297.3			296.9
3.500% Senior Notes, due 2027		495.3			494.8
6.25% Senior Notes, due 2037		228.1			228.1
4.250% Senior Notes, due 2047		591.7			591.5
Floating Rate Senior Notes, due 2020, interest rate of 2.55% and 3.30% at December 31, 2019 and 2018, respectively		299.7			299.0
Floating Rate Senior Notes, due 2019, interest rate of 3.29% at December 31, 2018		—			299.2
Trade Receivable Facility, interest rate of 2.42% and 3.07% at December 31, 2019 and 2018, respectively		340.0			390.0
Other notes		0.1			0.2
Total		2,773.6			3,120.4
Less: current maturities		(340.0	)		(390.0	)
Long-term debt	$	2,433.6		$	2,730.4

The Company’s 4.25% Senior Notes due 2024, 7% Debentures due 2025, 3.450% Senior Notes due 2027, 3.500% Senior Notes due 2027, 6.25% Senior Notes due 2037, 4.250% Senior Notes due 2047 and Floating Rate Senior Notes due 2020 (collectively, the “Senior Notes”) are senior unsecured obligations of the Company, ranking equal in right of payment with the Company’s existing and future unsubordinated indebtedness. Upon a change-of-control repurchase event and a resulting below-investment-grade credit rating, the Company would be required to make an offer to repurchase all outstanding Senior Notes, with the exception of the 7% Debentures due 2025, at a price in cash equal to 101% of the principal amount of the Senior Notes, plus any accrued and unpaid interest.

The Senior Notes are carried net of original issue discount, which is being amortized by the effective interest method over the life of the issue. With the exception of the Floating Rate Senior Notes, due 2020, the Senior Notes are redeemable prior to their respective maturity dates at a make-whole redemption price. The principal amount, effective interest rate and maturity date for the Senior Notes are as follows:

	Principal Amount (in millions)		Effective Interest Rate	Maturity Date
4.25% Senior Notes	$	400.0	4.25%	July 2, 2024
7% Debentures	$	125.0	7.12%	December 1, 2025
3.450% Senior Notes	$	300.0	3.47%	June 1, 2027
3.500% Senior Notes	$	500.0	3.53%	December 15, 2027
6.25% Senior Notes	$	230.0	6.45%	May 1, 2037
4.250% Senior Notes	$	600.0	4.27%	December 15, 2047
Floating Rate Senior Notes, due 2020	$	300.0	Three-month LIBOR + 0.65%	May 22, 2020

The Company has a credit agreement with JPMorgan Chase Bank, N.A., as Administrative Agent, Truist Bank, as successor by merger to SunTrust Bank and formerly known as Branch Banking and Trust Company (BB&T), Deutsche Bank Securities, Inc., and Wells Fargo Bank, N.A., as Co-Syndication Agents, and the lenders party thereto (the “Credit Agreement”), which provides for a $700.0 million five-year senior unsecured revolving facility (the “Revolving Facility”). Borrowings under the Revolving Facility bear interest, at the Company’s option, at rates based upon LIBOR or a base rate, plus, for each rate, a margin determined in accordance with a ratings-based pricing grid.

The Credit Agreement requires the Company’s ratio of consolidated debt-to-consolidated earnings before interest, taxes, depreciation, depletion and amortization (EBITDA), as defined, for the trailing-twelve months (the “Ratio”) to not exceed

3.50x as of the end of any fiscal quarter, provided that the Company may exclude from the Ratio debt incurred in connection with certain acquisitions during the quarter or three preceding quarters so long as the Ratio calculated without such exclusion does not exceed 3.75x. Additionally, if no amounts are outstanding under both the Revolving Facility and the trade receivable securitization facility (discussed later), consolidated debt, including debt for which the Company is a co-borrower (see Note O), may be reduced by the Company’s unrestricted cash and cash equivalents in excess of $50.0 million, such reduction not to exceed $200.0 million, for purposes of the covenant calculation. The Company was in compliance with the Ratio at December 31, 2019.

On December 5, 2019, the Company extended its Revolving Facility by one year. The Revolving Facility expires on December 5, 2024, with any outstanding principal amounts, together with interest accrued thereon, due in full on that date. Available borrowings under the Revolving Facility are reduced by any outstanding letters of credit issued by the Company under the Revolving Facility. At December 31, 2019 and 2018, the Company had $2.3 million of outstanding letters of credit issued under the Revolving Facility and $697.7 million available for borrowing under the Revolving Facility. The Company paid the bank group an upfront loan commitment fee that is being amortized over the life of the Revolving Facility. The Revolving Facility includes an annual facility fee.

The Company, through a wholly-owned special-purpose subsidiary, has a $400.0 million trade receivable securitization facility (the “Trade Receivable Facility”). On September 24, 2019, the Company extended the maturity to September 23, 2020. The Trade Receivable Facility, with Truist Bank, Regions Bank, PNC Bank, N.A., The Bank of Tokyo-Mitsubishi UFJ, Ltd., New York Branch, and certain other lenders that may become a party to the facility from time to time, is backed by eligible trade receivables, as defined. Borrowings are limited to the lesser of the facility limit or the borrowing base, as defined. These receivables are originated by the Company and then sold or contributed to the wholly-owned special-purpose subsidiary. The Company continues to be responsible for the servicing and administration of the receivables purchased by the wholly-owned special-purpose subsidiary. Borrowings under the Trade Receivable Facility bear interest at a rate equal to one-month LIBOR plus 0.725%, subject to change in the event that this rate no longer reflects the lender’s cost of lending. The Trade Receivable Facility contains a cross-default provision to the Company’s other debt agreements.

The Company’s long-term debt maturities for the five years following December 31, 2019, and thereafter are:

(in millions)
2020	$	340.0
2021		0.1
2022		0.1
2023		—
2024		696.7
Thereafter		1,736.7
Total	$	2,773.6

The 2020 Floating Rate Notes mature on May 22, 2020. The Company has classified these obligations as noncurrent long-term debt on the consolidated balance sheet as of December 31, 2019 as it has the ability and intent to refinance the notes on a long-term basis. For the debt maturity schedule, the 2020 Floating Rate Notes are included in 2024.

The Company has a $5.0 million short-term line of credit. No amounts were outstanding under this line of credit at December 31, 2019 or 2018.

Revenues and Gross Profit

12 Months Ended

Dec. 31, 2019

Revenues And Gross Profit [Abstract]

Revenues and Gross Profit

Note Q: Revenues and Gross Profit

The following tables, which are reconciled to consolidated amounts, provide total revenues and gross profit by line of business: Building Materials (further divided by product line) and Magnesia Specialties. Interproduct revenues represent sales from the aggregates product line to the ready mixed concrete and asphalt and paving product lines and sales from the cement product line to the ready mixed concrete product line. The Company’s two cold mix asphalt plants have been reclassified from the asphalt and paving product line to the aggregates product line. These operations did not represent a material amount of product revenues and gross profit. Prior year information has been reclassified to conform to the presentation of the Company’s current reportable product lines.

years ended December 31 (in millions) Total revenues	2019			2018			2017
Building Materials Business:
Products and services:
Aggregates	$	2,756.7		$	2,365.8		$	2,145.6
Cement		439.1			387.8			371.2
Ready Mixed Concrete		948.1			963.8			936.0
Asphalt and Paving		294.0			258.6			282.0
Less: Interproduct revenues		(265.5	)		(264.2	)		(264.0	)
Products and services		4,172.4			3,711.8			3,470.8
Freight		295.4			244.8			224.8
Total Building Materials Business		4,467.8			3,956.6			3,695.6
Magnesia Specialties:
Products and services		249.9			268.6			252.7
Freight		21.4			19.1			17.3
Total Magnesia Specialties		271.3			287.7			270.0
Consolidated total revenues	$	4,739.1		$	4,244.3		$	3,965.6

Gross profit (loss)
Building Materials Business:
Products and services:
Aggregates	$	807.9		$	608.4		$	602.3
Cement		143.4			126.2			117.0
Ready Mixed Concrete		78.8			74.2			91.6
Asphalt and Paving		50.7			51.3			62.1
Products and services		1,080.8			860.1			873.0
Freight		(0.2	)		0.2			2.6
Total Building Materials Business		1,080.6			860.3			875.6
Magnesia Specialties:
Products and services		99.4			102.9			94.1
Freight		(4.0	)		(4.2	)		(4.7	)
Total Magnesia Specialties		95.4			98.7			89.4
Corporate		3.0			7.6			6.9
Consolidated gross profit	$	1,179.0		$	966.6		$	971.9

Domestic and foreign total revenues are as follows:

years ended December 31 (in millions)	2019		2018		2017
Domestic	$	4,676.3	$	4,166.4	$	3,901.3
Foreign		62.8		77.9		64.3
Consolidated total revenues	$	4,739.1	$	4,244.3	$	3,965.6

Property, Plant and Equipment, Net

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Property, Plant and Equipment, Net

Note G: Property, Plant and Equipment, Net

December 31
(in millions)	2019			2018
Land and land improvements	$	1,135.0		$	1,089.6
Mineral reserves and interests		2,509.8			2,506.8
Buildings		163.4			162.1
Machinery and equipment		4,548.6			4,357.7
Construction in progress		258.4			178.7
Finance lease right-of-use assets		18.3			—
		8,633.5			8,294.9
Less: Accumulated depreciation, depletion and amortization		(3,427.5	)		(3,137.7	)
Total	$	5,206.0		$	5,157.2

Depreciation, depletion and amortization expense related to property, plant and equipment was $354.4 million, $326.1 million and $279.8 million for the years ended December 31, 2019, 2018 and 2017, respectively. Depreciation, depletion and amortization expense for 2019 includes amortization of right-of-use assets from finance leases and for 2018 and 2017 includes amortization of machinery and equipment under capital leases.

Interest expense of $5.1 million, $3.0 million and $3.6 million was capitalized during 2019, 2018 and 2017, respectively.

At December 31, 2019 and 2018, $49.7 million and $56.2 million, respectively, of the Building Materials business’ property, plant and equipment, net, were located in foreign countries, namely the Bahamas and Canada.

Leases

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Leases

Note M: Leases

The Company has leases, primarily for equipment, railcars, fleet vehicles, office space, land and information technology equipment and software. The Company’s leases have remaining lease terms of one year to 53 years, some of which may include options to extend the leases for up to 30 years, and some of which may include options to terminate the leases within one year.

Certain of the Company’s lease agreements include payments based upon variable rates, including, but not limited, to hours used, tonnage processed and factors related to indices. The Company’s lease agreements do not contain any material residual value guarantees or material restrictive covenants.

The components of lease cost are as follows:

year ended December 31 (in millions)	2019
Operating lease cost	$	80.9
Finance lease cost:
Amortization of right-of-use assets		3.4
Interest on lease liabilities		0.5
Variable lease cost		21.1
Short-term lease cost		33.0
Total lease cost	$	138.9

The Company has royalty agreements that are prescriptively excluded from the scope of ASC 842 and generally require royalty payments based on tons produced, tons sold or total sales dollars and also contain minimum payments. Royalty expense was $58.2 million for the year ended December 31, 2019.

The balance sheet classifications of operating and finance leases are as follows:

December 31 (in millions)	2019
Operating Leases:
Operating lease right-of-use assets	$	481.9

Current operating lease liabilities	$	52.7
Noncurrent operating lease liabilities		433.9
Total operating lease liabilities	$	486.6

Finance Leases:
Property, plant and equipment	$	18.3
Accumulated depreciation		(3.1	)
Property, plant and equipment, net	$	15.2

Other current liabilities	$	2.8
Other noncurrent liabilities		5.9
Total finance lease liabilities	$	8.7

The incremental borrowing rate range used was 2.1% to 5.5%. Weighted-average remaining lease terms and discount rates are as follows:

December 31	2019
Weighted-average remaining lease terms (years):
Operating leases		14.5
Finance leases		9.0

Weighted-average discount rates:
Operating leases	4.3%
Finance leases	5.2%

Future lease payments as of December 31, 2019 are as follows:

	Operating			Finance
(in millions)	Leases			Leases
2020	$	71.9		$	3.2
2021		58.9			1.9
2022		53.1			1.1
2023		49.2			0.8
2024		42.1			0.7
Thereafter		396.1			3.5
Total lease payments		671.3			11.2
Less: imputed interest		(184.7	)		(2.5	)
Present value of lease payments		486.6			8.7
Less: current lease obligations		(52.7	)		(2.8	)
Total long-term lease obligations	$	433.9		$	5.9

Leases entered into but not yet commenced as of December 31, 2019 are immaterial.

Subsequent to December 31, 2019, the Company entered into a lease for its corporate headquarters in Raleigh, North Carolina to commence in 2021. The agreement represents a 15-year lease with fixed rent payments totaling approximately $56 million over the term of the lease.

Lease disclosures for the years ended December 31, 2018 and 2017 prior to the adoption of ASC 842 are as follows:

Total lease expense for operating leases was $122.5 million and $90.7 million for the years ended December 31, 2018 and 2017, respectively. Total royalties, principally for leased properties, were $52.5 million and $51.8 million for the years ended December 31, 2018 and 2017, respectively. The Company also has capital lease obligations for machinery and equipment. Future minimum lease and royalty commitments for all noncancelable agreements and capital lease obligations as of December 31, 2018 were as follows:

(in millions)	Capital Leases			Operating Leases		Royalty Commitments
2019	$	3.7		$	106.0	$	14.6
2020		2.7			70.5		11.4
2021		1.7			60.4		10.3
2022		1.0			57.5		9.5
2023		0.7			56.5		8.1
Thereafter		3.9			318.1		66.0
Total		13.7		$	669.0	$	119.9
Less: imputed interest		(2.9	)
Present value of minimum lease payments		10.8
Less: current capital lease obligations		(3.2	)
Long-term capital lease obligations	$	7.6

Consolidated Statements of Comprehensive Earnings (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss arising during period, tax	$ (4.8)	$ (7.6)	$ (2.6)
Amortization of prior service credit, tax	(0.2)	(0.5)	(0.5)
Amortization of actuarial loss, tax	3.8	3.2	5.3
Amount recognized in net periodic pension cost due to settlement, tax	0.0	0.7	0.0
Amortization of terminated value of forward starting interest rate swap agreements into interest expense, tax	$ 0.0	$ 0.2	$ 0.6

Goodwill and Other Intangible Assets - Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 560.4	$ 560.4
Accumulated Amortization	(101.9)	(88.8)
Net Balance	458.5	471.6
Noncompetition agreements
Finite-Lived Intangible Assets [Line Items]
Gross Amount	6.3	6.3
Accumulated Amortization	(6.2)	(6.2)
Net Balance	0.1	0.1
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Amount	65.6	65.6
Accumulated Amortization	(30.4)	(25.6)
Net Balance	35.2	40.0
Operating Permits
Finite-Lived Intangible Assets [Line Items]
Gross Amount	459.0	459.0
Accumulated Amortization	(42.3)	(36.1)
Net Balance	416.7	422.9
Use Rights And Other
Finite-Lived Intangible Assets [Line Items]
Gross Amount	16.7	16.7
Accumulated Amortization	(12.1)	(11.2)
Net Balance	4.6	5.5
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Amount	12.8	12.8
Accumulated Amortization	(10.9)	(9.7)
Net Balance	$ 1.9	$ 3.1

Revenues and Gross Profit - Total Revenues and Gross Profit by Product Line (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Product Information [Line Items]
Total revenues	$ 4,739.1	$ 4,244.3	$ 3,965.6
Gross profit (loss)	1,179.0	966.6	971.9
Interproduct Revenues
Product Information [Line Items]
Total revenues	(265.5)	(264.2)	(264.0)
Corporate
Product Information [Line Items]
Gross profit (loss)	3.0	7.6	6.9
Building Materials Business
Product Information [Line Items]
Total revenues	4,467.8	3,956.6	3,695.6
Gross profit (loss)	1,080.6	860.3	875.6
Building Materials Business \| Operating Segments
Product Information [Line Items]
Total revenues	4,467.8	3,956.6	3,695.6
Gross profit (loss)	1,080.6	860.3	875.6
Building Materials Business \| Operating Segments \| Products and Services
Product Information [Line Items]
Total revenues	4,172.4	3,711.8	3,470.8
Gross profit (loss)	1,080.8	860.1	873.0
Magnesia Specialties \| Operating Segments
Product Information [Line Items]
Total revenues	271.3	287.7	270.0
Gross profit (loss)	95.4	98.7	89.4
Magnesia Specialties \| Operating Segments \| Products and Services
Product Information [Line Items]
Total revenues	249.9	268.6	252.7
Gross profit (loss)	99.4	102.9	94.1
Aggregates \| Building Materials Business \| Operating Segments \| Reportable Subsegments \| Products and Services
Product Information [Line Items]
Total revenues	2,756.7	2,365.8	2,145.6
Gross profit (loss)	807.9	608.4	602.3
Cement \| Building Materials Business \| Operating Segments \| Reportable Subsegments \| Products and Services
Product Information [Line Items]
Total revenues	439.1	387.8	371.2
Gross profit (loss)	143.4	126.2	117.0
Ready Mixed Concrete \| Building Materials Business \| Operating Segments \| Reportable Subsegments \| Products and Services
Product Information [Line Items]
Total revenues	948.1	963.8	936.0
Gross profit (loss)	78.8	74.2	91.6
Asphalt and Paving \| Building Materials Business \| Operating Segments \| Reportable Subsegments \| Products and Services
Product Information [Line Items]
Total revenues	294.0	258.6	282.0
Gross profit (loss)	50.7	51.3	62.1
Freight
Product Information [Line Items]
Total revenues	316.8	263.9	242.1
Freight \| Building Materials Business
Product Information [Line Items]
Total revenues	295.4	244.8	224.8
Freight \| Building Materials Business \| Operating Segments
Product Information [Line Items]
Total revenues	295.4	244.8	224.8
Gross profit (loss)	(0.2)	0.2	2.6
Freight \| Magnesia Specialties \| Operating Segments
Product Information [Line Items]
Total revenues	21.4	19.1	17.3
Gross profit (loss)	$ (4.0)	$ (4.2)	$ (4.7)

Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Long-term debt, carrying values	$ 2,773.6	$ 3,120.4
Long-term debt, fair values	$ 2,940.0	$ 3,010.0

Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total	$ 2,773.6	$ 3,120.4
Less: current maturities	(340.0)	(390.0)
Long-term debt	2,433.6	2,730.4
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total	397.0	396.4
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total	124.4	124.3
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total	297.3	296.9
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total	495.3	494.8
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total	228.1	228.1
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total	591.7	591.5
Floating Rate Senior Notes, Due 2020
Debt Instrument [Line Items]
Total	299.7	299.0
Floating Rate Senior Notes, Due 2019
Debt Instrument [Line Items]
Total		299.2
Trade Receivable Facility
Debt Instrument [Line Items]
Total	340.0	390.0
Other Notes
Debt Instrument [Line Items]
Total	$ 0.1	$ 0.2

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Note J: Income Taxes

The components of the Company’s income tax expense (benefit) are as follows:

years ended December 31 (in millions)	2019			2018			2017
Federal income taxes:
Current	$	83.9		$	15.3		$	129.2
Deferred		31.1			69.6			(239.3	)
Total federal income taxes		115.0			84.9			(110.1	)
State income taxes:
Current		20.5			6.0			14.8
Deferred		(1.5	)		14.1			(0.9	)
Total state income taxes		19.0			20.1			13.9
Foreign income taxes:
Current		2.8			(1.4	)		1.2
Deferred		(0.5	)		2.1			0.5
Total foreign income taxes		2.3			0.7			1.7
Income tax expense (benefit)	$	136.3		$	105.7		$	(94.5	)

On December 22, 2017, the U.S. government enacted the Tax Cuts and Jobs Act of 2017 (the 2017 Tax Act). The 2017 Tax Act included provisions that lowered the federal statutory corporate income tax rate from 35% to 21% beginning in 2018, imposed a one-time transition tax on mandatory deemed repatriation of undistributed net earnings and changed how foreign earnings are subject to U.S. tax. U.S. GAAP generally requires the effects of a tax law change to be recorded as a component of income tax expense in the period of enactment. However, the SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118), which allowed companies to record provisional amounts during a measurement period of up to one year from enactment where the necessary information was not available to complete the accounting for certain income tax effects of the 2017 Tax Act.

The Company recognized, on a provisional basis, a net tax benefit of $258.1 million related to the 2017 Tax Act for the remeasurement of deferred tax assets and liabilities in its consolidated financial statements for the year ended December 31, 2017. In accordance with the provisions of SAB 118, the Company completed the accounting for the impact of the 2017 Tax Act during the year ended December 31, 2018, and as a result recognized income tax expense of $1.1 million for the transition tax on mandatory deemed repatriation of undistributed foreign earnings; income tax expense of $1.5 million for the write-off of deferred tax assets that will not be realized due to changes in the deductibility of executive compensation; and an income tax benefit of $21.5 million primarily related to the accelerated deductions for pension funding, inventory and insurance prepayments that were claimed on the Company’s 2017 income tax returns.

For the year ended December 31, 2018, the benefit related to the utilization of federal net operating loss (NOL) carryforwards, reflected in current tax expense, was $5.8 million.

For the years ended December 31, 2019, 2018 and 2017, foreign pretax earnings were $15.1 million, $5.7 million and $10.6 million, respectively.

The Company’s effective income tax rate varied from the statutory United States income tax rate because of the following
tax differences:

years ended December 31	2019			2018			2017
Statutory income tax rate		21.0	%		21.0	%		35.0	%
(Reduction) increase resulting from:
Effect of statutory depletion		(3.4	)		(3.4	)		(5.6	)
State income taxes, net of federal tax benefit		2.0			2.8			1.5
Change in tax status of subsidiary		(1.7	)		—			—
Stock based compensation		(0.5	)		(0.5	)		(1.0	)
Impact from 2017 Tax Act		—			(3.3	)		(41.7	)
Domestic production deduction		—			—			(2.2	)
Other items		0.8			1.7			(1.3	)
Effective income tax rate		18.2	%		18.3	%		(15.3	%)

The statutory depletion deduction for all years is calculated as a percentage of sales, subject to certain limitations. Due to these limitations, the impact of changes in the sales volumes and earnings may not proportionately affect the Company’s statutory depletion deduction and the corresponding impact on the effective income tax rate.

The Company recognized a net tax benefit from the change in tax status of a subsidiary from a partnership to a corporation in 2019, which reduced income tax expense and increased consolidated net earnings by $15.2 million, or $0.24 per diluted share.

The Company was entitled to receive a 9% tax deduction related to income from domestic (i.e., United States) production activities in 2017. The deduction reduced income tax expense and increased consolidated net earnings by $15.5 million, or $0.25 per diluted share, in 2017. The domestic production deduction was eliminated by the 2017 Tax Act.

The principal components of the Company’s deferred tax assets and liabilities are as follows:

December 31	Deferred Assets (Liabilities)
(in millions)	2019			2018
Deferred tax assets related to:
Inventories	$	62.6		$	52.6
Valuation and other reserves		22.3			22.4
Net operating loss carryforwards		10.5			11.0
Accumulated other comprehensive loss		85.2			84.2
Lease liability		114.7			—
Other items, net		2.9			3.0
Gross deferred tax assets		298.2			173.2
Valuation allowance on deferred tax assets		(9.0	)		(8.6	)
Total net deferred tax assets		289.2			164.6
Deferred tax liabilities related to:
Property, plant and equipment		(700.8	)		(478.3	)
Goodwill and other intangibles		(151.7	)		(170.6	)
Right-of-use assets		(112.1	)		—
Partnerships and joint ventures		(27.4	)		(204.3	)
Employee benefits		(30.2	)		(17.0	)
Total deferred tax liabilities		(1,022.2	)		(870.2	)
Deferred income taxes, net	$	(733.0	)	$	(705.6	)

The Company had $4.1 million and $3.2 million of domestic federal NOL carryforwards at December 31, 2019 and 2018, respectively. The Company had domestic state NOL carryforwards of $161.0 million and $168.1 million at December 31, 2019

and 2018, respectively. These carryforwards have various expiration dates through 2039. At December 31, 2019 and 2018, deferred tax assets associated with these carryforwards were $10.5 million and $11.0 million, respectively, net of the federal benefit of the state deduction, for which valuation allowances of $9.0 million and $8.6 million, respectively, were recorded. The Company also had domestic state tax credit carryforwards of $1.1 million and $1.0 million at December 31, 2019 and 2018, respectively, which have various expiration dates through 2039. At December 31, 2019 and 2018, deferred tax assets associated with these carryforwards were $0.9 million and $0.8 million, respectively, net of the federal benefit of the state deduction.

Deferred tax liabilities for property, plant and equipment result from accelerated depreciation methods being used for income tax purposes as compared with the straight-line method for financial reporting purposes. The increase in 2019 compared with 2018 was primarily driven by the impact of 100% expensing of capital expenditures for tax purposes and by the change in the tax status of a subsidiary from a partnership to a corporation. The majority of the deferred tax liabilities recorded for the Company were related to property, plant and equipment.

Deferred tax liabilities for partnerships and joint ventures relate to the difference between the tax basis in partnerships and joint ventures when compared to the basis for financial reporting purposes. The decrease in 2019 compared with 2018 was a result of the change in the tax status of a subsidiary from a partnership to a corporation, which required the write-off of the deferred tax liability on the partnership investment, and the recording of deferred tax liabilities on the assets owned by the Company.

Deferred tax liabilities related to goodwill and other intangibles reflect the cessation of goodwill amortization for financial reporting purposes, while amortization continues for income tax purposes.

The Company expects to permanently reinvest the earnings from its wholly-owned Canadian and Bahamian subsidiaries, and accordingly, has not provided deferred taxes on the subsidiaries’ undistributed net earnings or basis differences. The Company believes that the tax liability that would be incurred upon repatriation is immaterial at December 31, 2019.

years ended December 31 (in millions)	2019			2018			2017
Unrecognized tax benefits at beginning of year	$	24.1		$	22.4		$	21.8
Gross increases – tax positions in prior years		0.4			0.9			1.4
Gross decreases – tax positions in prior years		—			—			(0.7	)
Gross increases – tax positions in current year		1.8			1.8			5.0
Gross decreases – tax positions in current year		(0.8	)		(1.0	)		(0.9	)
Lapse of statute of limitations		—			—			(4.2	)
Unrecognized tax benefits at end of year	$	25.5		$	24.1		$	22.4

Amount that, if recognized, would favorably impact the effective tax rate	$	15.5		$	12.8		$	10.4

Unrecognized tax benefits are reversed as a discrete event if an examination of applicable tax returns is not initiated by a federal or state tax authority within the statute of limitations or upon effective settlement with federal or state tax authorities. Management believes its accrual for unrecognized tax benefits is sufficient to cover uncertain tax positions reviewed during audits by taxing authorities.

The Company anticipates that it is reasonably possible that its unrecognized tax benefits may decrease up to $17.1 million, excluding interest and correlative effects, during the twelve months ending December 31, 2020, due to the expiration of the statutes of limitations for the 2016 and all prior open tax years.

For the year ended December 31, 2017, $3.9 million was reversed into income upon the statute of limitations expiration for the 2010 through 2013 tax years.

The Company’s tax years subject to federal, state or foreign examinations are 2011 through 2019.

Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Other intangibles acquired	$ 1.5
Amortization expense of intangible assets	$ 13.0	$ 13.9	$ 14.2

Other Operating (Income) and Expenses, Net

12 Months Ended

Dec. 31, 2019

Other Income And Expenses [Abstract]

Other Operating (Income) and Expenses, Net

Note S: Other Operating (Income) and Expenses, Net

Other operating income and expenses, net, are comprised generally of gains and losses on the sale of assets; asset and portfolio rationalization charges; recoveries and losses related to certain customer accounts receivable; rental, royalty and services income; accretion expense, depreciation expense and gains and losses related to asset retirement obligations. These net amounts represented income of $9.1 million in 2019, income of $18.2 million in 2018 and an expense of $0.8 million in 2017. 2019 income includes the reversal of $6.9 million of accruals for sales tax and unclaimed property contingencies. The 2018 amount reflects $18.8 million of asset and portfolio rationalization charges, offset by $7.7 million in net gains on legal settlements and $25.3 million in gains on the sale of assets, primarily excess land. The 2017 amount reflects $19.4 million of gains on the sale of assets, primarily excess land, offset by $12.7 million of nonrecurring repair costs related to certain of the Company’s leased railcars and $10.8 million of executive retirement expense.

The asset and portfolio rationalization charge relates to the Company’s Southwest ready mixed concrete operations reported in the West Group. This charge reflects the Company’s evaluation of the recoverability of certain long-lived assets, including property, plant and equipment and intangible assets, for underperforming operations in this business and a reduction in workforce. Of the total charge, $17.0 million was noncash and $1.8 million was settled in cash.

Consolidated Statements of Total Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Dividends declared	$ 2.06	$ 1.84	$ 1.72

Shareholders' Equity - Additional Information (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares authorized	100,000,000.0	100,000,000.0
Common stock, par value	$ 0.01	$ 0.01
Common stock reserved for issuance under stock-based award plans	1,500,000
Stock Repurchased During Period, Shares	400,000	500,000	500,000
Common stock remaining under repurchase authorization	13,700,000
Maximum
Class of Stock [Line Items]
Stock repurchase program, shares authorized to be repurchased	20,000,000.0

Revenue Recognition

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

Revenue Recognition

Note B: Revenue Recognition

Performance Obligations. Performance obligations are contractual promises to transfer or provide a distinct good or service for a stated price. The Company’s product sales agreements are single-performance obligations that are satisfied at a point in time. Performance obligations within paving service agreements are satisfied over time, primarily ranging from one day to two years. For product revenues and freight revenues, customer payment terms are generally 30 days from invoice date. Customer payments for the paving operations are based on a contractual billing schedule and are due 30 days from invoice date.

Future revenues from unsatisfied performance obligations at December 31, 2019, 2018 and 2017 were $136.1 million, $78.1 million and $67.0 million, respectively, where the remaining periods to complete these obligations ranged from three months to 12 months, two months to 22 months and one month to 23 months, respectively.

Sales Taxes. The Company is deemed to be an agent when collecting sales taxes from customers. Sales taxes collected are initially recorded as liabilities until remitted to taxing authorities and are not reflected in the consolidated statements of earnings as revenues and expenses.

Revenue by Category. The following table presents the Company’s total revenues by category for each reportable segment:

years ended December 31	Products and Services		Freight		Total
(in millions)	2019
Mid-America Group	$	1,328.8	$	117.2	$	1,446.0
Southeast Group		489.1		17.3		506.4
West Group		2,354.5		160.9		2,515.4
Total Building Materials Business		4,172.4		295.4		4,467.8
Magnesia Specialties		249.9		21.4		271.3
Total	$	4,422.3	$	316.8	$	4,739.1

	2018
Mid-America Group	$	1,133.8	$	89.4	$	1,223.2
Southeast Group		409.6		13.8		423.4
West Group		2,168.4		141.6		2,310.0
Total Building Materials Business		3,711.8		244.8		3,956.6
Magnesia Specialties		268.6		19.1		287.7
Total	$	3,980.4	$	263.9	$	4,244.3

	2017
Mid-America Group	$	982.2	$	71.1	$	1,053.3
Southeast Group		348.7		13.9		362.6
West Group		2,139.9		139.8		2,279.7
Total Building Materials Business		3,470.8		224.8		3,695.6
Magnesia Specialties		252.7		17.3		270.0
Total	$	3,723.5	$	242.1	$	3,965.6

Service revenues, which solely include the paving operations located in Colorado, were $250.6 million, $219.6 million and $245.3 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Contract Balances. Costs in excess of billings relate to the conditional right to consideration for completed contractual performance and are contract assets on the consolidated balance sheets. Costs in excess of billings are reclassified to accounts receivable when the right to consideration becomes unconditional. Billings in excess of costs relate to customers invoiced in advance of contractual performance and are contract liabilities on the consolidated balance sheets. The following table presents information about the Company’s contract balances:

December 31
(in millions)	2019		2018
Costs in excess of billings	$	2.8	$	2.0
Billings in excess of costs	$	7.8	$	6.7

Revenues recognized from the beginning balance of contract liabilities for the years ended December 31, 2019 and 2018 were $6.6 million and $6.8 million, respectively.

Retainage, which primarily relates to the paving services, represents amounts that have been billed to customers but payment withheld until final acceptance of the performance obligation by the customer. Included on the Company’s consolidated balance sheets, retainage was $10.2 million and $7.5 million at December 31, 2019 and 2018, respectively.

Policy Elections. When the Company arranges third-party freight to deliver products to customers, the Company has elected the delivery to be a fulfillment activity rather than a separate performance obligation. Further, the Company acts as a principal in the delivery arrangements and, as required by the revenue standard, the related revenues and costs are presented gross and are included in the consolidated statements of earnings.

Goodwill and Other Intangible Assets - Intangible Assets Deemed to Indefinite Life that are Therefore Not Amortized (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	$ 28.3	$ 29.7
Operating Permits
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	6.6	6.6
Use Rights Not Subject To Amortization
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	19.0	20.3
Trade names
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	2.7	2.8
Building Materials Business
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	25.8	27.2
Building Materials Business \| Operating Permits
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	6.6	6.6
Building Materials Business \| Use Rights Not Subject To Amortization
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	19.0	20.3
Building Materials Business \| Trade names
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	0.2	0.3
Magnesia Specialties
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	2.5	2.5
Magnesia Specialties \| Trade names
Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite life intangible assets	$ 2.5	$ 2.5

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Fair Values of Pension Plan Assets by Asset Class and Fair Value Hierarchy Level (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	$ 868.0	$ 717.9
Quoted Prices In Active Markets For Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	3.0	2.9
Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	865.0	715.0
Mid-sized to Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	262.5	196.5
Mid-sized to Large Cap \| Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	262.5	196.5
Small Cap, International and Emerging Growth Funds
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	290.3	210.4
Small Cap, International and Emerging Growth Funds \| Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	290.3	210.4
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	242.9	228.2
Debt Securities \| Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	242.9	228.2
Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	42.9	35.5
Real Estate \| Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	42.9	35.5
Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	26.4	44.4
Hedge Funds \| Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	26.4	44.4
Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	3.0	2.9
Cash Equivalents \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	$ 3.0	$ 2.9

Revenues and Gross Profit (Tables)

12 Months Ended

Dec. 31, 2019

Revenues And Gross Profit [Abstract]

Total Revenues and Gross Profit by Product Line

years ended December 31 (in millions) Total revenues	2019			2018			2017
Building Materials Business:
Products and services:
Aggregates	$	2,756.7		$	2,365.8		$	2,145.6
Cement		439.1			387.8			371.2
Ready Mixed Concrete		948.1			963.8			936.0
Asphalt and Paving		294.0			258.6			282.0
Less: Interproduct revenues		(265.5	)		(264.2	)		(264.0	)
Products and services		4,172.4			3,711.8			3,470.8
Freight		295.4			244.8			224.8
Total Building Materials Business		4,467.8			3,956.6			3,695.6
Magnesia Specialties:
Products and services		249.9			268.6			252.7
Freight		21.4			19.1			17.3
Total Magnesia Specialties		271.3			287.7			270.0
Consolidated total revenues	$	4,739.1		$	4,244.3		$	3,965.6

Gross profit (loss)
Building Materials Business:
Products and services:
Aggregates	$	807.9		$	608.4		$	602.3
Cement		143.4			126.2			117.0
Ready Mixed Concrete		78.8			74.2			91.6
Asphalt and Paving		50.7			51.3			62.1
Products and services		1,080.8			860.1			873.0
Freight		(0.2	)		0.2			2.6
Total Building Materials Business		1,080.6			860.3			875.6
Magnesia Specialties:
Products and services		99.4			102.9			94.1
Freight		(4.0	)		(4.2	)		(4.7	)
Total Magnesia Specialties		95.4			98.7			89.4
Corporate		3.0			7.6			6.9
Consolidated gross profit	$	1,179.0		$	966.6		$	971.9

Domestic and Foreign Total Revenues

Domestic and foreign total revenues are as follows:

years ended December 31 (in millions)	2019		2018		2017
Domestic	$	4,676.3	$	4,166.4	$	3,901.3
Foreign		62.8		77.9		64.3
Consolidated total revenues	$	4,739.1	$	4,244.3	$	3,965.6

SCHEDULE II - Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2019

Valuation And Qualifying Accounts [Abstract]

SCHEDULE II - Valuation and Qualifying Accounts

SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS

MARTIN MARIETTA MATERIALS, INC. AND CONSOLIDATED SUBSIDIARIES

Col A	Col B		Col C					Col D			Col E
			Additions
Description	Balance at beginning of period		(1) Charged to costs and expenses		(2) Charged to other accounts- describe			Deductions- describe			Balance at end of period
	(Amounts in Millions)
Year ended December 31, 2019
Allowance for doubtful accounts	$	3.3	$	1.4	$	—		$	—		$	4.7
Allowance for uncollectible notes receivable		—		—		—			—			—
Inventory valuation allowance		159.2		38.8		—			29.4	^(a)		168.6

Year ended December 31, 2018
Allowance for doubtful accounts	$	2.4	$	0.9	$	—		$	—		$	3.3
Allowance for uncollectible notes receivable		0.2		—		—			0.2	^(b)		—
Inventory valuation allowance		144.0		36.9		5.1	^(c)		26.8	^(a)		159.2

Year ended December 31, 2017
Allowance for doubtful accounts	$	6.3	$	—	$	—		$	3.9	^(b)	$	2.4
Allowance for uncollectible notes receivable		0.4		—		—			0.2	^(b)		0.2
Inventory valuation allowance		134.9		38.5		—			29.4	^(a)		144.0

^(a)	Sale of reserved inventory and divestitures

^(b)	Write-off of uncollectible accounts and change in estimates

^(c)	Application of reserve policy to acquired inventories

Leases - Summary of Future Lease Payments (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Operating Leases
2020	$ 71.9
2021	58.9
2022	53.1
2023	49.2
2024	42.1
Thereafter	396.1
Total lease payments	671.3
Less: imputed interest	(184.7)
Present value of lease payments	486.6
Less: current lease obligations	(52.7)
Total long-term lease obligations	433.9
Financing Leases
2020	3.2
2021	1.9
2022	1.1
2023	0.8
2024	0.7
Thereafter	3.5
Total lease payments	11.2
Less: imputed interest	(2.5)
Total finance lease liabilities	8.7
Less: current lease obligations	(2.8)
Other noncurrent liabilities	$ 5.9

Goodwill and Other Intangible Assets - Changes in Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Balance at beginning of period	$ 2,399.1	$ 2,160.3
Measurement period adjustments	(1.6)
Acquisitions		245.3
Goodwill allocated to assets held for sale	(0.2)	(5.6)
Divestitures	(0.5)	(0.9)
Balance at end of period	2,396.8	2,399.1
Mid-America Group
Goodwill [Line Items]
Balance at beginning of period	431.9	281.4
Measurement period adjustments	(1.0)
Acquisitions		150.5
Balance at end of period	430.9	431.9
Southeast Group
Goodwill [Line Items]
Balance at beginning of period	144.2	50.3
Measurement period adjustments	(0.6)
Acquisitions		94.8
Goodwill allocated to assets held for sale	(0.2)
Divestitures		(0.9)
Balance at end of period	143.4	144.2
West Group
Goodwill [Line Items]
Balance at beginning of period	1,823.0	1,828.6
Goodwill allocated to assets held for sale		(5.6)
Divestitures	(0.5)
Balance at end of period	$ 1,822.5	$ 1,823.0

Supplemental Cash Flow Information

12 Months Ended

Dec. 31, 2019

Supplemental Cash Flow Elements [Abstract]

Supplemental Cash Flow Information

Note R: Supplemental Cash Flow Information

Noncash investing and financing activities are as follows:

years ended December 31
(in millions)	2019		2018		2017
Accrued liabilities for purchases of property, plant and equipment	$	54.2	$	67.0	$	61.6
Acquisition of assets through asset exchange	$	2.4	$	—	$	2.5
Remeasurement of operating lease right-of-use assets	$	2.0	$	—	$	—
Right-of-use assets obtained in exchange for new operating lease liabilities	$	45.7	$	—	$	—
Right-of-use assets obtained in exchange for new finance lease liabilities	$	0.2	$	—	$	—
Acquisition of assets through capital lease	$	—	$	1.1	$	0.8
Sale of asset to settle liability	$	—	$	—	$	0.9

Supplemental disclosures of cash flow information are as follows:

years ended December 31
(in millions)	2019		2018		2017
Cash paid for interest, net of amount capitalized	$	127.9	$	137.2	$	78.9
Cash paid for income taxes	$	101.7	$	28.9	$	155.8
Cash paid for amounts included in the measurement of lease liabilities¹:
Operating cash flows used for operating leases	$	76.1
Operating cash flows used for finance leases	$	0.5
Financing cash flows used for finance leases	$	11.0

¹	These disclosures are required by ASC 842, which was adopted on January 1, 2019.

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended				228 Months Ended	288 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of incentive compensation to acquire shares, maximum	50.00%
Percentage of discount rate to market value on the incentive compensation	20.00%
Company normal retirement age	62 years
Common stock price	$ 279.64				$ 279.64	$ 279.64
Aggregate intrinsic values of options exercised	$ 21.6	$ 12.4	$ 13.2
Aggregate intrinsic values for options outstanding	10.0				$ 10.0	$ 10.0
Aggregate intrinsic values for options exercisable	$ 10.0				$ 10.0	$ 10.0
Awards available for grant	742,000				742,000	742,000
Additional shares issuance under the plan				800,000
Texas Industries Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options issued to former option holders	821,282
Number of options issued per single option	0.7
Employee stock options expiration period	90 days
Options granted in 2015 and 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock options expiration date	10 years
Options granted prior to 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock options expiration date	8 years
Incentive Compensation Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of stock awards, granted	$ 192.27	$ 212.12	$ 208.68
Aggregate intrinsic values for stock awards	$ 4.8				$ 4.8	$ 4.8
Common stock price	$ 279.64				$ 279.64	$ 279.64
Aggregate intrinsic values of stock awards, distributed	$ 1.5	$ 1.7	$ 2.6
Awards granted	21,883
Restricted Stock - Service Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of stock awards, granted	$ 196.91	$ 211.03	$ 213.76
Awards granted	86,922
Restricted Stock - Performance Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of stock awards, granted	$ 192.27	$ 212.12	$ 207.73
Awards granted	49,644
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic values for stock awards	$ 86.2				$ 86.2	$ 86.2
Aggregate intrinsic values of stock awards, distributed	49.8	$ 23.0	$ 15.8
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefits for stock options exercised	$ 2.0	$ 1.7	$ 3.5
Common stock issued under the plan	0	0	0
Legacy TXI plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards available for grant	0				0	0
Shareholder Value Achievement Plan (1996)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance							250,000
Common stock issued under the plan						42,025
Awards granted					0
Directors' Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	300,000				300,000	300,000
Common stock issued under the plan	2,756	3,105	2,132

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000.0	100,000,000.0
Common stock, shares outstanding	62,400,000	62,500,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000.0	10,000,000.0
Preferred stock, shares outstanding	0	0

Retirement Plans, Postretirement and Postemployment Benefits (Tables)

12 Months Ended

Dec. 31, 2019

Fair Values of Pension Plan Assets by Asset Class and Fair Value Hierarchy Level

The fair values of pension plan assets by asset class and fair value hierarchy level are as follows:

	Fair Value Measurements
December 31		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Net Asset Value		Total Fair Value
(in millions)		2019
Equity securities¹:
Mid-sized to large cap		$	—	$	—	$	—	$	262.5	$	262.5
Small cap, international and emerging growth funds			—		—		—		290.3		290.3
Debt securities¹:
Core fixed income			—		—		—		242.9		242.9
Real estate			—		—		—		42.9		42.9
Hedge funds			—		—		—		26.4		26.4
Cash equivalents			3.0		—		—		—		3.0
Total		$	3.0	$	—	$	—	$	865.0	$	868.0

		2018
Equity securities¹:
Mid-sized to large cap		$	—	$	—	$	—	$	196.5	$	196.5
Small cap, international and emerging growth funds			—		—		—		210.4		210.4
Debt securities¹:
Core fixed income			—		—		—		228.2		228.2
Real estate			—		—		—		35.5		35.5
Hedge funds			—		—		—		44.4		44.4
Cash equivalents			2.9		—		—		—		2.9
Total		$	2.9	$	—	$	—	$	715.0	$	717.9

¹	These investments are common collective investment trusts valued using the net asset value (NAV) unit price provided by the fund administrator. The NAV is based on the value of the underlying assets owned by the fund.

Schedule of Assumed Health Care Cost Trend Rates

Assumed health care cost trend rates at December 31 are:

	2019	2018
Health care cost trend rate assumed for next year	6.75%	7.0%
Rate to which the cost trend rate gradually declines	4.75%	5.0%
Year the rate reaches the ultimate rate	2028	2023

Schedule of One Percentage-Point Change in Assumed Health Care Cost Trend Rates

A one percentage-point change in assumed health care cost trend rates would have the following effects:

	One Percentage Point
(in millions)	Increase		(Decrease)
Total service and interest cost components	$	—	$	—
Postretirement benefit obligation	$	0.7	$	(0.6	)

Pension

Schedule of Components of Net Periodic Benefit Cost (Credit)

The net periodic retirement benefit cost of defined benefit plans includes the following components:

years ended December 31 (in millions)	2019			2018			2017
Service cost	$	30.8		$	31.7		$	26.9
Interest cost		37.6			33.2			36.1
Expected return on assets		(47.9	)		(46.0	)		(39.8	)
Amortization of:
Prior service cost		—			0.1			0.3
Actuarial loss		16.0			12.8			14.1
Settlement charge		—			2.9			—
Net periodic benefit cost	$	36.5		$	34.7		$	37.6

Schedule of Recognized Comprehensive Earnings

The Company recognized the following amounts in consolidated comprehensive earnings:

years ended December 31
(in millions)	2019			2018			2017
Actuarial loss	$	11.7		$	32.1		$	13.3
Net prior service cost		6.4			—			—
Amortization of:
Prior service cost		—			(0.1	)		(0.3	)
Actuarial loss		(16.0	)		(12.8	)		(14.1	)
Settlement charge		—			(2.9	)		—
Total	$	2.1		$	16.3		$	(1.1	)

Schedule of Net Periodic Benefit Credit or Cost Not Yet Recognized

Accumulated other comprehensive loss includes the following amounts that have not yet been recognized in net periodic benefit cost:

December 31	2019				2018
(in millions)	Gross		Net of tax		Gross		Net of tax
Prior service cost	$	6.4	$	4.0	$	—	$	—
Actuarial loss		229.4		144.5		233.7		146.6
Total	$	235.8	$	148.5	$	233.7	$	146.6

Schedule of Change in Projected Benefit Obligation

The defined benefit plans’ change in projected benefit obligation is as follows:

years ended December 31
(in millions)	2019			2018
Net projected benefit obligation at beginning of year	$	847.9		$	879.3
Service cost		30.8			31.7
Interest cost		37.6			33.2
Actuarial loss (gain)		95.2			(54.6	)
Plan amendments		6.4			—
Gross benefits paid		(40.1	)		(41.7	)
Net projected benefit obligation at end of year	$	977.8		$	847.9

Schedule of Change In Plan Assets

The Company’s change in plan assets, funded status and amounts recognized on the Company’s consolidated balance sheets are as follows:

years ended December 31
(in millions)	2019			2018
Fair value of plan assets at beginning of year	$	717.9		$	638.1
Actual return on plan assets, net		131.3			(40.8	)
Employer contributions		58.9			162.3
Gross benefits paid		(40.1	)		(41.7	)
Fair value of plan assets at end of year	$	868.0		$	717.9

Schedule of Funded Status

December 31
(in millions)	2019			2018
Funded status of the plan at end of year	$	(109.8	)	$	(130.0	)
Accrued benefit cost	$	(109.8	)	$	(130.0	)

Schedule of Amounts Recognized on Consolidated Balance Sheets

December 31
(in millions)	2019			2018
Amounts recognized on consolidated balance sheets consist of:
Current liability	$	(6.4	)	$	(9.0	)
Noncurrent liability		(103.4	)		(121.0	)
Net amount recognized at end of year	$	(109.8	)	$	(130.0	)

Schedule of Accumulated Benefit Obligations in Excess of Plan Assets

Benefit obligations and fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets are as follows:

December 31
(in millions)	2019		2018
Projected benefit obligation	$	107.1	$	98.7
Accumulated benefit obligation	$	96.4	$	85.5
Fair value of plan assets	$	0.6	$	0.6

Schedule of Weighted-Average Assumptions

Weighted-average assumptions used to determine benefit obligations as of December 31 are:

	2019	2018
Discount rate	3.69%	4.38%
Rate of increase in future compensation levels	4.50%	4.50%

Weighted-average assumptions used to determine net periodic benefit cost for the years ended December 31 are:

	2019	2018	2017
Discount rate	4.38%	3.76%	4.29%
Rate of increase in future compensation levels	4.50%	4.50%	4.50%
Expected long-term rate of return on assets	6.75%	6.75%	6.75%

Schedule of Target Assets Allocation

The target allocation for 2019 and the actual pension plan asset allocation by asset class are as follows:

	Percentage of Plan Assets
		2019
		Target	December 31
Asset Class		Allocation	2019	2018
Equity securities		56%	64%	57%
Debt securities		30%	28%	32%
Hedge funds		4%	3%	6%
Real estate		10%	5%	5%
Total		100%	100%	100%

Schedule of Expected Benefit Payments

The expected benefit payments to be paid from plan assets for each of the next five years and the five-year period thereafter are as follows:

(in millions)
2020	$	43.5
2021	$	44.8
2022	$	46.2
2023	$	47.6
2024	$	50.9
Years 2025 - 2029	$	271.0

Postretirement Benefits

Schedule of Components of Net Periodic Benefit Cost (Credit)

The net periodic postretirement benefit credit for postretirement plans includes the following components:

years ended December 31
(in millions)	2019			2018			2017
Service cost	$	0.1		$	0.1		$	0.1
Interest cost		0.6			0.5			0.7
Amortization of:
Prior service credit		(0.8	)		(2.1	)		(1.7	)
Actuarial gain		(0.5	)		(0.2	)		(0.4	)
Total net periodic benefit credit	$	(0.6	)	$	(1.7	)	$	(1.3	)

Schedule of Recognized Comprehensive Earnings

The Company recognized the following amounts in consolidated comprehensive earnings:

years ended December 31
(in millions)	2019		2018			2017
Actuarial loss (gain)	$	1.0	$	(1.7	)	$	1.2
Net prior service credit		—		—			(3.9	)
Amortization of:
Prior service credit		0.8		2.1			1.7
Actuarial gain		0.5		0.2			0.4
Total	$	2.3	$	0.6		$	(0.6	)

Schedule of Net Periodic Benefit Credit or Cost Not Yet Recognized

Accumulated other comprehensive loss includes the following amounts that have not yet been recognized in net periodic benefit credit:

December 31	2019						2018
(in millions)	Gross			Net of tax			Gross			Net of tax
Prior service credit	$	(3.0	)	$	(1.9	)	$	(3.8	)	$	(2.4	)
Actuarial gain		(2.7	)		(1.7	)		(4.2	)		(2.7	)
Total	$	(5.7	)	$	(3.6	)	$	(8.0	)	$	(5.1	)

Schedule of Change in Projected Benefit Obligation

The postretirement health care plans’ change in benefit obligation is as follows:

years ended December 31
(in millions)	2019			2018
Net benefit obligation at beginning of year	$	13.3		$	15.3
Service cost		0.1			0.1
Interest cost		0.6			0.5
Participants’ contributions		1.2			0.3
Actuarial loss (gain)		1.0			(1.6	)
Gross benefits paid		(3.2	)		(1.3	)
Net benefit obligation at end of year	$	13.0		$	13.3

Schedule of Change In Plan Assets

The postretirement health care plans’ change in plan assets, funded status and amounts recognized on the Company’s consolidated balance sheets are as follows:

years ended December 31
(in millions)	2019			2018
Fair value of plan assets at beginning of year	$	—		$	—
Employer contributions		2.0			1.0
Participants’ contributions		1.2			0.3
Gross benefits paid		(3.2	)		(1.3	)
Fair value of plan assets at end of year	$	—		$	—

Schedule of Funded Status

December 31
(in millions)	2019			2018
Funded status of the plan at end of year	$	(13.0	)	$	(13.3	)
Accrued benefit cost	$	(13.0	)	$	(13.3	)

Schedule of Amounts Recognized on Consolidated Balance Sheets

December 31
(in millions)	2019			2018
Amounts recognized on consolidated balance sheets consist of:
Current liability	$	(2.0	)	$	(1.0	)
Noncurrent liability		(11.0	)		(12.3	)
Net amount recognized at end of year	$	(13.0	)	$	(13.3	)

Schedule of Weighted-Average Assumptions

Weighted-average assumptions used to determine the postretirement benefit obligation as of December 31 are:

		2019			2018
Discount rate		3.29%			4.15%

Weighted-average assumptions used to determine net postretirement benefit credit for the years ended December 31 are:

		2019			2018			2017
Discount rate		4.15%			3.47%			3.78%

Schedule of Expected Benefit Payments

The total expected benefit payments to be paid by the Company, net of participant contributions, for each of the next five years and the five-year period thereafter are as follows:

(in millions)
2020	$	2.0
2021	$	1.4
2022	$	1.4
2023	$	1.3
2024	$	1.2
Years 2025 - 2029	$	4.7

Commitments and Contingencies - Changes in Asset Retirement Obligations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Balance at beginning of year	$ 121.8	$ 109.7
Accretion expense	5.6	5.1
Liabilities incurred and liabilities assumed in business combinations	0.6	4.6
Liabilities settled	(1.2)	(2.8)
Revisions in estimated cash flows	17.1	5.2
Balance at end of year	$ 143.9	$ 121.8

Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2019

Revenue From Contract With Customer [Abstract]

Schedule of Company's Total Revenues by Category for each Reportable Segment

The following table presents the Company’s total revenues by category for each reportable segment:

years ended December 31	Products and Services		Freight		Total
(in millions)	2019
Mid-America Group	$	1,328.8	$	117.2	$	1,446.0
Southeast Group		489.1		17.3		506.4
West Group		2,354.5		160.9		2,515.4
Total Building Materials Business		4,172.4		295.4		4,467.8
Magnesia Specialties		249.9		21.4		271.3
Total	$	4,422.3	$	316.8	$	4,739.1

	2018
Mid-America Group	$	1,133.8	$	89.4	$	1,223.2
Southeast Group		409.6		13.8		423.4
West Group		2,168.4		141.6		2,310.0
Total Building Materials Business		3,711.8		244.8		3,956.6
Magnesia Specialties		268.6		19.1		287.7
Total	$	3,980.4	$	263.9	$	4,244.3

	2017
Mid-America Group	$	982.2	$	71.1	$	1,053.3
Southeast Group		348.7		13.9		362.6
West Group		2,139.9		139.8		2,279.7
Total Building Materials Business		3,470.8		224.8		3,695.6
Magnesia Specialties		252.7		17.3		270.0
Total	$	3,723.5	$	242.1	$	3,965.6

Summary of Information About the Company's Contract Balances

The following table presents information about the Company’s contract balances:

December 31
(in millions)	2019		2018
Costs in excess of billings	$	2.8	$	2.0
Billings in excess of costs	$	7.8	$	6.7

Leases - Summary of Weighted-average Remaining Lease Terms and Discount Rates (Detail)	Dec. 31, 2019
Weighted-average remaining lease terms (years):
Operating leases	14 years 6 months
Finance leases	9 years
Weighted-average discount rates:
Operating leases	4.30%
Finance leases	5.20%

Retirement Plans, Postretirement and Postemployment Benefits - Change in Projected Benefit Obligation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	$ 1.0	$ (1.6)
Pension
Defined Benefit Plan Disclosure [Line Items]
Net projected benefit obligation at beginning of year	847.9	879.3
Service cost	30.8	31.7	$ 26.9
Interest cost	37.6	33.2	36.1
Actuarial loss (gain)	95.2	(54.6)
Plan amendments	6.4
Gross benefits paid	(40.1)	(41.7)
Net projected benefit obligation at end of year	977.8	847.9	879.3
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net projected benefit obligation at beginning of year	13.3	15.3
Service cost	0.1	0.1	0.1
Interest cost	0.6	0.5	0.7
Participants' contributions	1.2	0.3
Gross benefits paid	(3.2)	(1.3)
Net projected benefit obligation at end of year	$ 13.0	$ 13.3	$ 15.3

Leases (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Summary of Components of Lease Cost

The components of lease cost are as follows:

year ended December 31 (in millions)	2019
Operating lease cost	$	80.9
Finance lease cost:
Amortization of right-of-use assets		3.4
Interest on lease liabilities		0.5
Variable lease cost		21.1
Short-term lease cost		33.0
Total lease cost	$	138.9

Summary of Balance Sheet Classifications of Operating and Finance Leases

The balance sheet classifications of operating and finance leases are as follows:

December 31 (in millions)	2019
Operating Leases:
Operating lease right-of-use assets	$	481.9

Current operating lease liabilities	$	52.7
Noncurrent operating lease liabilities		433.9
Total operating lease liabilities	$	486.6

Finance Leases:
Property, plant and equipment	$	18.3
Accumulated depreciation		(3.1	)
Property, plant and equipment, net	$	15.2

Other current liabilities	$	2.8
Other noncurrent liabilities		5.9
Total finance lease liabilities	$	8.7

Summary of Weighted-average Remaining Lease Terms and Discount Rates

Weighted-average remaining lease terms and discount rates are as follows:

December 31	2019
Weighted-average remaining lease terms (years):
Operating leases		14.5
Finance leases		9.0

Weighted-average discount rates:
Operating leases	4.3%
Finance leases	5.2%

Summary of Future Lease Payments

Future lease payments as of December 31, 2019 are as follows:

	Operating			Finance
(in millions)	Leases			Leases
2020	$	71.9		$	3.2
2021		58.9			1.9
2022		53.1			1.1
2023		49.2			0.8
2024		42.1			0.7
Thereafter		396.1			3.5
Total lease payments		671.3			11.2
Less: imputed interest		(184.7	)		(2.5	)
Present value of lease payments		486.6			8.7
Less: current lease obligations		(52.7	)		(2.8	)
Total long-term lease obligations	$	433.9		$	5.9

Summary of Future Minimum Lease and Royalty Commitments for all Noncancelable Agreements and Capital Lease Obligations

Future minimum lease and royalty commitments for all noncancelable agreements and capital lease obligations as of December 31, 2018 were as follows:

(in millions)	Capital Leases			Operating Leases		Royalty Commitments
2019	$	3.7		$	106.0	$	14.6
2020		2.7			70.5		11.4
2021		1.7			60.4		10.3
2022		1.0			57.5		9.5
2023		0.7			56.5		8.1
Thereafter		3.9			318.1		66.0
Total		13.7		$	669.0	$	119.9
Less: imputed interest		(2.9	)
Present value of minimum lease payments		10.8
Less: current capital lease obligations		(3.2	)
Long-term capital lease obligations	$	7.6

Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets related to:
Inventories	$ 62.6	$ 52.6
Valuation and other reserves	22.3	22.4
Net operating loss carryforwards	10.5	11.0
Accumulated other comprehensive loss	85.2	84.2	$ 80.1
Lease liability	114.7
Other items, net	2.9	3.0
Gross deferred tax assets	298.2	173.2
Valuation allowance on deferred tax assets	(9.0)	(8.6)
Total net deferred tax assets	289.2	164.6
Deferred tax liabilities related to:
Property, plant and equipment	(700.8)	(478.3)
Goodwill and other intangibles	(151.7)	(170.6)
Right-of-use assets	(112.1)
Partnerships and joint ventures	(27.4)	(204.3)
Employee benefits	(30.2)	(17.0)
Total deferred tax liabilities	(1,022.2)	(870.2)
Deferred income taxes, net	$ (733.0)	$ (705.6)

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of One Percentage-Point Change In Assumed Health Care Cost Trend Rate (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Compensation And Retirement Disclosure [Abstract]
Postretirement benefit obligation, Increase	$ 0.7
Postretirement benefit obligation, Decrease	$ (0.6)

Business Combinations - Business Acquisition, Pro Forma Information (Details) - Bluegrass Materials Company - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Total revenues	$ 4,299.7	$ 4,178.6
Net earnings attributable to Martin Marietta	$ 489.5	$ 691.7
Diluted earnings per share	$ 7.75	$ 10.94

Stock-Based Compensation - Summary Information for Restricted Stock Awards and Incentive Compensation Stock Awards (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock - Service Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Awards, January 1, 2019	278,147
Number of Awards, Awarded	86,922
Number of Awards, Distributed	(171,689)
Number of Awards, Forfeited	(9,441)
Number of Awards, December 31, 2019	183,939	278,147
Weighted-Average Grant-Date Fair Value, January 1, 2019	$ 158.29
Weighted-Average Grant-Date Fair Value, Awarded	196.91	$ 211.03	$ 213.76
Weighted-Average Grant-Date Fair Value, Distributed	148.72
Weighted-Average Grant-Date Fair Value, Forfeited	166.51
Weighted-Average Grant-Date Fair Value, December 31, 2019	$ 185.06	$ 158.29
Restricted Stock - Performance Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Awards, January 1, 2019	151,939
Number of Awards, Awarded	49,644
Number of Awards, Distributed	(54,424)
Number of Awards, Forfeited	(5,329)
Number of Awards, Adjustment for performance	(17,609)
Number of Awards, December 31, 2019	124,221	151,939
Weighted-Average Grant-Date Fair Value, January 1, 2019	$ 174.74
Weighted-Average Grant-Date Fair Value, Awarded	192.27	$ 212.12	207.73
Weighted-Average Grant-Date Fair Value, Distributed	133.73
Weighted-Average Grant-Date Fair Value, Forfeited	205.21
Weighted-Average Grant-Date Fair Value, Adjustment for performance	133.77
Weighted-Average Grant-Date Fair Value, December 31, 2019	$ 204.21	$ 174.74
Incentive Compensation Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Awards, January 1, 2019	35,376
Number of Awards, Awarded	21,883
Number of Awards, Distributed	(15,948)
Number of Awards, Forfeited	(1,727)
Number of Awards, December 31, 2019	39,584	35,376
Weighted-Average Grant-Date Fair Value, January 1, 2019	$ 206.55
Weighted-Average Grant-Date Fair Value, Awarded	192.27	$ 212.12	$ 208.68
Weighted-Average Grant-Date Fair Value, Distributed	206.23
Weighted-Average Grant-Date Fair Value, Forfeited	205.54
Weighted-Average Grant-Date Fair Value, December 31, 2019	$ 198.83	$ 206.55

Inventories, Net (Tables)

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Schedule of Inventories Net

December 31 (in millions)	2019			2018
Finished products	$	643.6		$	615.7
Products in process		41.9			35.6
Raw materials		32.4			31.3
Supplies and expendable parts		141.5			139.6
		859.4			822.2
Less: Allowances		(168.6	)		(159.2	)
Total	$	690.8		$	663.0

Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense	$ 129.3	$ 137.1	$ 91.5
Tax effect	136.3	105.7	(94.5)
Earnings from Continuing Operations	11.1	10.5	8.5
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	11.1	10.2	7.7
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations		0.3	0.8
Reclassification out of Accumulated Other Comprehensive Income \| Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Settlement charge		2.9
Prior service credit	(0.8)	(2.0)	(1.4)
Actuarial loss	15.5	12.7	13.8
Tax effect	(3.6)	(3.4)	(4.7)
Earnings from Continuing Operations	11.1	10.2	7.7
Reclassification out of Accumulated Other Comprehensive Income \| Pension and Postretirement Benefit Plans \| Other Nonoperating Expenses and (Income), Net
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications out of accumulated other comprehensive loss before taxes	$ 14.7	13.6	12.4
Reclassification out of Accumulated Other Comprehensive Income \| Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense		0.5	1.4
Tax effect		(0.2)	(0.6)
Earnings from Continuing Operations		$ 0.3	$ 0.8

Goodwill and Other Intangible Assets - Estimated Amortization Expense of Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
2020	$ 13.2
2021	12.5
2022	11.1
2023	10.6
2024	10.6
Thereafter	400.5
Net Balance	$ 458.5	$ 471.6

Commitments and Contingencies - Contractual Purchase Commitments (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 140.6
2021	15.0
2022	3.0
2023	0.9
2024	0.9
Thereafter	15.9
Total	$ 176.3

Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Accounting Policies

Note A: Accounting Policies

Organization. Martin Marietta (the “Company”) is a natural resource-based building materials company. The Company supplies aggregates (crushed stone, sand and gravel) through its network of more than 300 quarries, mines and distribution yards in 27 states, Canada and the Bahamas. In the western United States, Martin Marietta also provides cement and downstream products, namely, ready mixed concrete, asphalt and paving services, in markets where the Company also has a leading aggregates position. Specifically, the Company has two cement plants and several cement distribution facilities in Texas and Louisiana, and 141 ready mixed concrete plants and seven asphalt plants in Texas, Colorado, Louisiana, Arkansas and Wyoming. Paving services are exclusively in Colorado. The Company’s heavy-side building materials are used in infrastructure, nonresidential and residential construction projects. Aggregates are also used in agricultural, utility and environmental applications and as railroad ballast. The aggregates, cement, ready mixed concrete and asphalt and paving product lines are reported collectively as the “Building Materials” business. As of December 31, 2019, the Building Materials business contains the following reportable segments: Mid-America Group, Southeast Group and West Group. The Mid-America Group operates in Indiana, Iowa, northern Kansas, Kentucky, Maryland, Minnesota, Missouri, eastern Nebraska, North Carolina, Ohio, Pennsylvania, South Carolina, Virginia, Washington and West Virginia. The Southeast Group has operations in Alabama, Florida, Georgia, southwestern South Carolina, Tennessee, Nova Scotia and the Bahamas. The West Group operates in Arkansas, Colorado, southern Kansas, Louisiana, western Nebraska, Nevada, Oklahoma, Texas, Utah and Wyoming. In addition to these operations, the Company sells to customers in New York, Delaware, New Mexico and Mississippi. The following states accounted for 72% of the Building Materials business’ 2019 total products and services revenues: Texas, Colorado, North Carolina, Georgia and Iowa.

The Company also operates a Magnesia Specialties business, which produces magnesia-based chemical products used in industrial, agricultural and environmental applications, and dolomitic lime sold primarily to customers in the steel and mining industries. Magnesia Specialties’ production facilities are located in Ohio and Michigan, and products are shipped to customers worldwide.

Basis of Presentation and Use of Estimates. The Company’s consolidated financial statements are presented in conformity with accounting principles generally accepted in the United States (U.S. GAAP), which requires management to make certain estimates and assumptions about future events. These estimates and the underlying assumptions affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities and reported amounts of revenues and expenses. Such estimates include the valuation of accounts receivable, inventories, goodwill, intangible assets and other long-lived assets and assumptions used in the calculation of income tax expense (benefit), retirement and other postemployment benefits, stock-based compensation, the allocation of the purchase price to the fair values of assets acquired and liabilities assumed as part of business combinations and revenue recognition for service contracts. These estimates and assumptions are based on management’s judgment. Management evaluates estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, and adjusts such estimates and assumptions when facts and circumstances dictate. Changes in credit, equity and energy markets and changes in construction activity increase the uncertainty inherent in certain estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from estimates. Changes in estimates, including those resulting from continuing changes in the economic environment, are reflected in the consolidated financial statements for the period in which the change in estimate occurs.

During the year ended December 31, 2019, the Company identified a prior-period error that overstated its earnings from a nonconsolidated equity affiliate. The overstatement was not deemed material to the current period or any previously reported periods and was therefore corrected as an out-of-period expense of $15.7 million. The pretax noncash adjustment is recorded in other nonoperating expenses, consistent with the recurring classification of equity earnings from the nonconsolidated affiliate.

Basis of Consolidation. The consolidated financial statements include the accounts of the Company and its wholly-owned and majority-owned subsidiaries. Partially-owned affiliates are either consolidated or accounted for at cost or as equity investments, depending on the level of ownership interest or the Company’s ability to exercise control over the affiliates’ operations. Intercompany balances and transactions between subsidiaries have been eliminated in consolidation.

Revenue Recognition. Total revenues include sales of products and services provided to customers, net of discounts or allowances, if any, and include freight and delivery costs billed to customers. Revenues for product sales are recognized when control of the promised good is transferred to unaffiliated customers, typically when finished products are shipped. Revenues derived from the paving business are recognized using the percentage-of-completion method under the cost-to-cost approach. Under the cost-to-cost approach, recognized contract revenue is determined by multiplying the total estimated contract revenue by the estimated percentage of completion. Contract costs are recognized as incurred. The percentage of completion is determined on a contract-by-contract basis using project costs incurred to date as a percentage of total estimated project costs. The Company believes the cost-to-cost approach is appropriate, as the use of asphalt in a paving contract is relatively consistent with the performance of the related paving services. Paving contracts, notably with governmental entities, may contain performance bonuses based on quality specifications. Given the uncertainty of meeting the criteria until the performance obligation is completed, performance bonuses are recognized as revenues when and if determined to be achieved. Performance bonuses were not material to the Company’s consolidated results of operations for the years ended December 31, 2019, 2018 and 2017. Freight revenues reflect delivery arranged by the Company using a third party on behalf of the customer and are recognized consistently with the timing of the product revenues.

Freight and Delivery Costs. Freight and delivery costs represent pass-through transportation costs incurred and paid by the Company to third-party carriers to deliver products to customers. These costs are then billed to the customers.

Cash and Cash Equivalents. Cash equivalents are comprised of highly-liquid instruments with original maturities of three months or less from the date of purchase. The Company manages its cash and cash equivalents to ensure short-term operating cash needs are met and excess funds are managed efficiently. When operating cash is not sufficient to meet current needs, the Company borrows money under its credit facilities. The Company utilizes excess cash to either pay down credit facility borrowings or invest in money market funds, money market demand deposit accounts or offshore time deposit accounts. Money market demand deposits and offshore time deposit accounts are exposed to bank solvency risk.

Accounts Receivable. Accounts receivable are stated at cost. The Company does not typically charge interest on customer accounts receivable. The Company records an allowance for doubtful accounts, which includes a provision for probable losses based on historical write-offs and a specific reserve for accounts deemed at risk. The Company writes-off accounts receivable when it becomes probable, based upon customer facts and circumstances, that such amounts will not be collected.

Inventories Valuation. Inventories are stated at the lower of cost or net realizable value. Costs for finished products and in process inventories are determined by the first-in, first-out method. Carrying value for parts and supplies are determined by the weighted-average cost method. The Company records an allowance for finished product inventories based on an analysis of inventory on hand in excess of historical sales for a twelve-month or five-year average period and future demand. The Company also establishes an allowance for parts over five years old and supplies over one year old.

Post-production stripping costs, which represent costs of removing overburden and waste materials to access mineral deposits, are a component of inventory production costs and recognized as incurred.

Property, Plant and Equipment. Property, plant and equipment are stated at cost.

The estimated service lives for property, plant and equipment are as follows:

Class of Assets		Range of Service Lives
Buildings		5 to 20 years
Machinery & Equipment		2 to 20 years
Land Improvements		5 to 60 years

The Company begins capitalizing quarry development costs at a point when reserves are determined to be proven or probable, economically mineable and when demand supports investment in the market. Capitalization of these costs ceases when production commences. Capitalized quarry development costs are classified as land improvements and depreciated over the life of the reserves.

The Company reviews relevant facts and circumstances to determine whether to capitalize or expense pre-production stripping costs when additional pits are developed at an existing quarry. If the additional pit operates in a separate and distinct area of the quarry, these costs are capitalized as quarry development costs and depreciated over the life of the uncovered reserves. Additionally, a separate asset retirement obligation is created for additional pits when the liability is incurred. Once a pit enters the production phase, all post-production stripping costs are charged to inventory production costs as incurred.

Mineral reserves and mineral interests acquired in connection with a business combination are valued using an income approach over the life of the reserves.

Depreciation is computed based on estimated service lives using the straight-line method. Depletion of mineral reserves is calculated based on proven and probable reserves using the units-of-production method on a quarry-by-quarry basis.

Property, plant and equipment are reviewed for impairment whenever facts and circumstances indicate that the carrying amount of an asset group may not be recoverable. An impairment loss is recognized if expected future undiscounted cash flows over the estimated remaining service life of the related asset are less than the asset’s carrying value.

Repair and Maintenance Costs. Repair and maintenance costs that do not substantially extend the life of the Company’s plant and equipment are expensed as incurred.

Leases. Effective January 1, 2019, if the Company determines a contract is or contains a lease at inception of the agreement, the Company records right-of-use (ROU) assets, which represent the Company’s right to use an underlying leased asset, and lease liabilities, which represent the Company’s obligation to make lease payments arising from the lease, on the consolidated balance sheet at the present value of the future lease payments over the lease term at commencement date. The Company determines the present value of lease payments based on the implicit rate, which may be explicitly stated in the lease, if available, or may be the Company’s estimated collateralized incremental borrowing rate based on the term of the lease. Initial ROU assets also include any lease payments made at or before commencement date and any initial direct costs incurred and exclude lease incentives. Certain of the Company’s leases contain renewal and/or termination options. The Company recognizes renewal or termination options as part of its ROU assets and lease liabilities when the Company has the unilateral right to renew or terminate and it is reasonably certain these options will be exercised.

Some leases require the Company pay non-lease components, which may include taxes, maintenance, insurance and certain other expenses applicable to the leased property, and are primarily considered variable costs. The Company accounts for lease and non-lease components as a single amount, with the exception of railcar and fleet vehicle leases, for which the Company separately accounts for the lease and non-lease components.

Leases are evaluated and determined to be operating or finance leases. If a lease transfers ownership to the underlying asset by the end of the lease term; includes a purchase option that is reasonably certain to be exercised; has a lease term for the major part of the remaining economic life of the underlying asset; has a present value of the sum of the lease payments that equals or exceeds substantially all of the fair value of the underlying asset; is for an underlying asset that is of a specialized nature and is expected to have no alternative use to the lessor at the end of the lease term, the lease is a finance lease. If none of these terms exist, the lease is an operating lease.

As allowed by Accounting Standards Codification 842, Leases (ASC 842), leases with an initial lease term of one year or less are not recorded on the balance sheet. Costs for these leases are expensed as incurred.

In the consolidated statements of earnings, operating lease expense, which is recognized on a straight-line basis over the lease term, and the amortization of finance lease ROU assets are included in cost of revenues or selling, general and administrative expenses. Accretion on the liabilities for finance leases is included in interest expense.

Goodwill and Intangible Assets. Goodwill represents the excess purchase price paid for acquired businesses over the estimated fair value of identifiable assets and liabilities. Other intangibles represent amounts assigned principally to contractual agreements and are amortized ratably over periods based on related contractual terms. If an intangible asset is deemed to have an indefinite life, it is not amortized.

The Company’s reporting units, which represent the level at which goodwill is tested for impairment, are based on the operating segments of the Building Materials business. Goodwill is assigned to the respective reporting unit(s) based on the location of acquisitions at the time of consummation. Goodwill is tested for impairment by comparing each reporting unit’s fair value to its carrying value, which represents a Step 1 approach. However, prior to Step 1, the Company may perform an optional qualitative assessment and evaluate macroeconomic conditions, industry and market conditions, cost factors, overall financial performance and other business or reporting unit-specific events. If the Company concludes it is more-likely-than-not (i.e., a likelihood of more than 50%) that a reporting unit’s fair value is higher than its carrying value, the Company does not perform any further goodwill impairment testing for that reporting unit. Otherwise, the Company proceeds to Step 1 of its goodwill impairment analysis. The Company may bypass the qualitative assessment for any reporting unit in any period and proceed directly with the quantitative calculation in Step 1. If the reporting unit’s fair value exceeds its carrying value, no further calculation is necessary. A reporting unit with a carrying value in excess of its fair value constitutes a Step 1 failure and will lead to an impairment charge.

The carrying values of goodwill and other indefinite-lived intangible assets are reviewed annually, as of October 1, for impairment. An interim review is performed between annual tests if facts and circumstances indicate potential impairment. The carrying value of other amortizable intangibles is reviewed if facts and circumstances indicate potential impairment. If a review indicates the carrying value is impaired, a charge is recorded.

Retirement Plans and Postretirement Benefits. The Company sponsors defined benefit retirement plans and also provides other postretirement benefits. The Company recognizes the funded status, defined as the difference between the fair value of plan assets and the benefit obligation, of its pension plans and other postretirement benefits as an asset or liability on the consolidated balance sheets. Actuarial gains or losses that arise during the year are recognized as a component of accumulated other comprehensive earnings or loss. Those amounts are amortized over the participants’ average remaining service period and recognized as a component of net periodic benefit cost. The amount amortized is determined using a corridor approach and represents the excess over 10% of the greater of the projected benefit obligation or pension
plan assets.

Insurance Reserves. The Company has insurance coverage with large deductibles for workers’ compensation, automobile liability, marine liability and general liability claims, and is also self-insured for health claims. The Company records insurance reserves based on an actuarial-determined analysis, which calculates development factors that are applied to total case reserves within the insurance programs. While the Company believes the assumptions used to calculate these liabilities are appropriate, significant differences in actual experience and/or significant changes in these assumptions may materially affect insurance costs.

Stock-Based Compensation. The Company has stock-based compensation plans for employees and its Board of Directors. The Company recognizes all forms of stock-based awards that vest as compensation expense. The compensation expense is the fair value of the awards at the measurement date and is recognized over the requisite service period. Forfeitures are recognized as they occur.

The fair value of restricted stock awards, incentive compensation stock awards and Board of Directors’ fees paid in the form of common stock are based on the closing price of the Company’s common stock on the awards’ respective grant dates. The fair value of performance stock awards as of the grant dates is determined by a Monte Carlo simulation methodology.

In 2019, 2018 and 2017, the Company did not issue any stock options. For stock options issued prior to 2016, the Company used the accelerated expense recognition method. The accelerated recognition method requires stock options that vest ratably to be divided into tranches. The expense for each tranche is allocated to its particular vesting period.

Environmental Matters. The Company records a liability for an asset retirement obligation at fair value in the period in which it is incurred. The asset retirement obligation is recorded at the acquisition date of a long-lived tangible asset if the fair value can be reasonably estimated. A corresponding amount is capitalized as part of the asset’s carrying amount. The fair value is affected by management’s assumptions regarding the scope of the work required, inflation rates and quarry closure dates.

Further, the Company records an accrual for other environmental remediation liabilities in the period in which it is probable that a liability has been incurred and the appropriate amounts can be estimated reasonably. Such accruals are adjusted as further information develops or circumstances change. Generally, these costs are not discounted to their present value or offset for potential insurance or other claims or potential gains from future alternative uses for a site.

Income Taxes. Deferred income taxes, net, on the consolidated balance sheets reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes, net of valuation allowances. The effect on deferred income tax assets and liabilities attributable to changes in enacted tax rates are charged or credited to income tax expense or benefit in the period of enactment.

Uncertain Tax Positions. The Company recognizes a tax benefit when it is more-likely-than-not, based on the technical merits, that a tax position would be sustained upon examination by a taxing authority. The amount to be recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. The Company’s unrecognized tax benefits are recorded in other liabilities on the consolidated balance sheets or as an offset to the deferred tax asset for tax carryforwards
where available.

The Company records interest accrued in relation to unrecognized tax benefits as income tax expense. Penalties, if incurred, are recorded as operating expenses in the consolidated statements of earnings.

Sales Taxes. Sales taxes collected from customers are recorded as liabilities until remitted to taxing authorities and therefore are not reflected in the consolidated statements of earnings.

Start-Up Costs. Noncapital start-up costs for new facilities and products are charged to operations as incurred.

Warranties. The Company’s construction contracts usually contain warranty provisions covering defects in materials, design or workmanship, the majority of which cover one year after project completion. Due to the nature of its projects, including contract owner inspections of the work both during construction and prior to acceptance, the Company has not experienced material warranty costs for these short-term warranties and therefore does not believe an accrual for these costs is necessary. The ready mixed concrete product line carries a longer warranty period, for which the Company has accrued an estimate of warranty cost based on experience with the type of work and any known risks relative to the projects. These costs were not material to the Company’s consolidated results of operations for the years ended December 31, 2019, 2018 and 2017.

Consolidated Comprehensive Earnings and Accumulated Other Comprehensive Loss. Consolidated comprehensive earnings for the Company consist of consolidated net earnings, adjustments for the funded status of pension and postretirement benefit plans, foreign currency translation adjustments and the amortization of the value of terminated forward starting interest rate swap agreements into interest expense, and are presented in the Company’s consolidated statements of comprehensive earnings.

Accumulated other comprehensive loss consists of unrecognized gains and losses related to the funded status of the pension and postretirement benefit plans, foreign currency translation and the unamortized value of terminated forward starting interest rate swap agreements, and is presented on the Company’s consolidated balance sheets.

The components of the changes in accumulated other comprehensive loss and related cumulative noncurrent deferred tax assets are as follows:

	Pension and Postretirement Benefit Plans			Foreign Currency			Unamortized Value of Terminated Forward Starting Interest Rate Swap			Total
years ended December 31 (in millions)	2019
Accumulated other comprehensive loss at beginning of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Other comprehensive (loss) earnings before reclassifications, net of tax		(14.5	)		1.2			—			(13.3	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		11.1			—			—			11.1
Other comprehensive (loss) earnings, net of tax		(3.4	)		1.2			—			(2.2	)
Accumulated other comprehensive loss at end of period	$	(144.9	)	$	(0.9	)	$	—		$	(145.8	)
Cumulative noncurrent deferred tax assets at end of period	$	85.2		$	—		$	—		$	85.2

	2018
Accumulated other comprehensive loss at beginning of period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Other comprehensive loss before reclassifications, net of tax		(22.9	)		(2.1	)		—			(25.0	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		10.2			—			0.3			10.5
Other comprehensive (loss) earnings, net of tax		(12.7	)		(2.1	)		0.3			(14.5	)
Accumulated other comprehensive loss at end of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Cumulative noncurrent deferred tax assets at end of period	$	84.2		$	—		$	—		$	84.2

	2017
Accumulated other comprehensive loss at beginning of period	$	(128.4	)	$	(1.2	)	$	(1.1	)	$	(130.7	)
Other comprehensive (loss) earnings before reclassifications, net of tax		(8.1	)		1.2			—			(6.9	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		7.7			—			0.8			8.5
Other comprehensive (loss) earnings, net of tax		(0.4	)		1.2			0.8			1.6
Accumulated other comprehensive loss at end of period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Cumulative noncurrent deferred tax assets at end of period	$	79.9		$	—		$	0.2		$	80.1

Reclassifications out of accumulated other comprehensive loss are as follows:

years ended December 31 (in millions)	2019			2018			2017			Affected line items in the consolidated statements of earnings
Pension and postretirement benefit plans:
Settlement charge	$	—		$	2.9		$	—
Amortization of:
Prior service credit		(0.8	)		(2.0	)		(1.4	)
Actuarial loss		15.5			12.7			13.8
		14.7			13.6			12.4		Other nonoperating expenses and (income), net
Tax effect		(3.6	)		(3.4	)		(4.7	)	Income tax expense (benefit)
Total	$	11.1		$	10.2		$	7.7
Unamortized value of terminated forward starting interest rate swap:
Additional interest expense	$	—		$	0.5		$	1.4		Interest expense
Tax effect		—			(0.2	)		(0.6	)	Income tax expense (benefit)
Total	$	—		$	0.3		$	0.8

Earnings Per Common Share. The Company computes earnings per common share (EPS) pursuant to the two-class method. The two-class method determines EPS for each class of common stock and participating securities according to dividends or dividend equivalents and their respective participation rights in undistributed earnings. The Company paid nonforfeitable dividend equivalents during the vesting period on its restricted stock awards and incentive stock awards made prior to 2016, which results in these being considered participating securities.

The numerator for basic and diluted earnings per common share is net earnings attributable to Martin Marietta, reduced by dividends and undistributed earnings attributable to the Company’s unvested restricted stock awards and incentive stock awards issued prior to 2016. The denominator for basic earnings per common share is the weighted-average number of common shares outstanding during the period. Diluted earnings per common share is computed assuming that the weighted-average number of common shares is increased by the conversion, using the treasury stock method, of awards issued to employees and nonemployee members of the Company’s Board of Directors under certain stock-based compensation arrangements if the conversion is dilutive.

The following table reconciles the numerator and denominator for basic and diluted earnings per common share:

years ended December 31 (in millions)	2019		2018		2017
Net earnings attributable to Martin Marietta	$	611.9	$	470.0	$	713.3
Less: Distributed and undistributed earnings attributable to unvested participating securities		0.9		0.8		2.0
Basic and diluted net earnings attributable to common shareholders attributable to Martin Marietta	$	611.0	$	469.2	$	711.3

Basic weighted-average common shares outstanding		62.5		62.9		62.9
Effect of dilutive employee and director awards		0.2		0.2		0.3
Diluted weighted-average common shares outstanding		62.7		63.1		63.2

Reclassifications. Certain reclassifications were made to the comparative years’ financial statements and notes to the financial statements to conform to the December 31, 2019 presentation. Such reclassifications had no impact on the Company’s previously reported results of operations, financial position or cash flows.

New Accounting Pronouncements

Leases

Effective January 1, 2019, the Company adopted ASC 842, which applies to virtually all leases, excluding mineral interest royalty agreements. ASC 842 requires the modified retrospective transition approach, applying the new standard to all leases existing at the date of initial application. It further states that an entity may use either 1) its effective date or 2) the beginning of the earliest comparative period presented in the financial statements as its date of initial application. The Company used the effective date as the date of initial application. As such, financial information and disclosures required under ASC 842 are not provided for dates and periods prior to January 1, 2019.

The lease standard provides a number of practical expedients for transition accounting. The Company elected the “package of practical expedients”, which permitted the Company to not reassess its prior conclusions about lease identification, lease classification and initial direct costs. The Company elected the practical expedients pertaining to the use of hindsight and to land easements. Applying the hindsight practical expedient resulted in longer lease terms for many leases.

The adoption of ASC 842 resulted in the recognition of ROU assets and lease liabilities of $502.5 million and $501.6 million, respectively, for operating leases and $10.9 million and $12.1 million, respectively, for finance leases. The adoption did not have a material impact on the Company’s consolidated statement of earnings or consolidated statement of cash flows.

Pending Accounting Pronouncements

Credit Losses

In June 2016, the Financial Accounting Standards Board issued Accounting Standards Update (ASU) 2016-13, Financial Instruments – Credit Losses (“ASU 2016-13”), which is effective and will be adopted January 1, 2020. ASU 2016-13 includes a current expected credit loss (CECL) model that requires an entity to estimate credit losses expected over the life of an exposure or pool of exposures based on historical information, current information and reasonable and supportable forecasts at the time the asset is recognized and is remeasured at each reporting period. ASU 2016-13 primarily relates to the Company’s receivables, but the scope also includes retainage and contract assets related to its paving business. The Company has evaluated ASU 2016-13, and the adoption will not have a material impact on its financial position or consolidated statement of earnings and comprehensive earnings.

Property, Plant and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Property, Plant and Equipment, Net

December 31
(in millions)	2019			2018
Land and land improvements	$	1,135.0		$	1,089.6
Mineral reserves and interests		2,509.8			2,506.8
Buildings		163.4			162.1
Machinery and equipment		4,548.6			4,357.7
Construction in progress		258.4			178.7
Finance lease right-of-use assets		18.3			—
		8,633.5			8,294.9
Less: Accumulated depreciation, depletion and amortization		(3,427.5	)		(3,137.7	)
Total	$	5,206.0		$	5,157.2

Property, Plant and Equipment, Net - Property, Plant and Equipment, Net (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Land and land improvements	$ 1,135.0	$ 1,089.6
Mineral reserves and interests	2,509.8	2,506.8
Buildings	163.4	162.1
Machinery and equipment	4,548.6	4,357.7
Construction in progress	258.4	178.7
Finance lease right-of-use assets	18.3
Gross property, plant and equipment	8,633.5	8,294.9
Less: Accumulated depreciation, depletion and amortization	(3,427.5)	(3,137.7)
Total	$ 5,206.0	$ 5,157.2

Business Combinations - Summary of the Estimated Fair Values of the Assets Acquired and the Liabilities Assumed (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Apr. 27, 2018	Dec. 31, 2017
Assets:
Goodwill	$ 2,396.8	$ 2,399.1		$ 2,160.3
Bluegrass Materials Company
Assets:
Cash and cash equivalents			$ 1.2
Receivables			25.5
Inventory			46.6
Other current assets			1.0
Property, plant and equipment			1,519.3
Intangible assets, other than goodwill			20.2
Goodwill			243.0
Total Assets			1,856.8
Liabilities:
Accounts payable and accrued expenses			17.9
Deferred income tax liabilities, net			212.5
Noncontrolling interest			9.0
Total Liabilities			239.4
Total Consideration			$ 1,617.4

Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Organization

Basis of Presentation and Use of Estimates

Basis of Consolidation

Revenue Recognition

Freight and Delivery Costs

Cash and Cash Equivalents

Accounts Receivable

Inventories Valuation

Post-production stripping costs, which represent costs of removing overburden and waste materials to access mineral deposits, are a component of inventory production costs and recognized as incurred.

Property, Plant and Equipment

Property, Plant and Equipment. Property, plant and equipment are stated at cost.

The estimated service lives for property, plant and equipment are as follows:

Class of Assets		Range of Service Lives
Buildings		5 to 20 years
Machinery & Equipment		2 to 20 years
Land Improvements		5 to 60 years

Mineral reserves and mineral interests acquired in connection with a business combination are valued using an income approach over the life of the reserves.

Repair and Maintenance Costs

Repair and Maintenance Costs. Repair and maintenance costs that do not substantially extend the life of the Company’s plant and equipment are expensed as incurred.

Leases

Goodwill and Intangible Assets

Retirement Plans and Postretirement Benefits

Insurance Reserves

Stock-Based Compensation

Environmental Matters

Income Taxes

Uncertain Tax Positions

Sales Taxes

Sales Taxes. Sales taxes collected from customers are recorded as liabilities until remitted to taxing authorities and therefore are not reflected in the consolidated statements of earnings.

Start-Up Costs

Start-Up Costs. Noncapital start-up costs for new facilities and products are charged to operations as incurred.

Warranties

Consolidated Comprehensive Earnings and Accumulated Other Comprehensive Loss

The components of the changes in accumulated other comprehensive loss and related cumulative noncurrent deferred tax assets are as follows:

	Pension and Postretirement Benefit Plans			Foreign Currency			Unamortized Value of Terminated Forward Starting Interest Rate Swap			Total
years ended December 31 (in millions)	2019
Accumulated other comprehensive loss at beginning of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Other comprehensive (loss) earnings before reclassifications, net of tax		(14.5	)		1.2			—			(13.3	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		11.1			—			—			11.1
Other comprehensive (loss) earnings, net of tax		(3.4	)		1.2			—			(2.2	)
Accumulated other comprehensive loss at end of period	$	(144.9	)	$	(0.9	)	$	—		$	(145.8	)
Cumulative noncurrent deferred tax assets at end of period	$	85.2		$	—		$	—		$	85.2

	2018
Accumulated other comprehensive loss at beginning of period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Other comprehensive loss before reclassifications, net of tax		(22.9	)		(2.1	)		—			(25.0	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		10.2			—			0.3			10.5
Other comprehensive (loss) earnings, net of tax		(12.7	)		(2.1	)		0.3			(14.5	)
Accumulated other comprehensive loss at end of period	$	(141.5	)	$	(2.1	)	$	—		$	(143.6	)
Cumulative noncurrent deferred tax assets at end of period	$	84.2		$	—		$	—		$	84.2

	2017
Accumulated other comprehensive loss at beginning of period	$	(128.4	)	$	(1.2	)	$	(1.1	)	$	(130.7	)
Other comprehensive (loss) earnings before reclassifications, net of tax		(8.1	)		1.2			—			(6.9	)
Amounts reclassified from accumulated other comprehensive loss, net of tax		7.7			—			0.8			8.5
Other comprehensive (loss) earnings, net of tax		(0.4	)		1.2			0.8			1.6
Accumulated other comprehensive loss at end of period	$	(128.8	)	$	—		$	(0.3	)	$	(129.1	)
Cumulative noncurrent deferred tax assets at end of period	$	79.9		$	—		$	0.2		$	80.1

Reclassifications out of accumulated other comprehensive loss are as follows:

years ended December 31 (in millions)	2019			2018			2017			Affected line items in the consolidated statements of earnings
Pension and postretirement benefit plans:
Settlement charge	$	—		$	2.9		$	—
Amortization of:
Prior service credit		(0.8	)		(2.0	)		(1.4	)
Actuarial loss		15.5			12.7			13.8
		14.7			13.6			12.4		Other nonoperating expenses and (income), net
Tax effect		(3.6	)		(3.4	)		(4.7	)	Income tax expense (benefit)
Total	$	11.1		$	10.2		$	7.7
Unamortized value of terminated forward starting interest rate swap:
Additional interest expense	$	—		$	0.5		$	1.4		Interest expense
Tax effect		—			(0.2	)		(0.6	)	Income tax expense (benefit)
Total	$	—		$	0.3		$	0.8

Earnings Per Common Share

The following table reconciles the numerator and denominator for basic and diluted earnings per common share:

years ended December 31 (in millions)	2019		2018		2017
Net earnings attributable to Martin Marietta	$	611.9	$	470.0	$	713.3
Less: Distributed and undistributed earnings attributable to unvested participating securities		0.9		0.8		2.0
Basic and diluted net earnings attributable to common shareholders attributable to Martin Marietta	$	611.0	$	469.2	$	711.3

Basic weighted-average common shares outstanding		62.5		62.9		62.9
Effect of dilutive employee and director awards		0.2		0.2		0.3
Diluted weighted-average common shares outstanding		62.7		63.1		63.2

Reclassifications

New Accounting Pronouncements

Leases

Pending Accounting Pronouncements

Credit Losses

Commitments and Contingencies - Schedule of Future Minimum Contracts of Affreightment and Royalty Commitments for All Noncancelable Agreements (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
2020	$ 15.8
2021	16.1
2022	16.3
2023	16.6
2024	16.9
Thereafter	52.2
Total	133.9
2020	15.7
2021	11.1
2022	10.3
2023	9.2
2024	8.9
Thereafter	59.7
Total	$ 114.9	$ 119.9

Goodwill and Other Intangible Assets

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Goodwill and Other Intangible Assets

Note C: Goodwill and Other Intangible Assets

The following table shows the changes in goodwill by reportable segment and in total:

December 31	Mid- America Group			Southeast Group			West Group			Total
(in millions)	2019
Balance at beginning of period	$	431.9		$	144.2		$	1,823.0		$	2,399.1
Measurement period adjustments		(1.0	)		(0.6	)		—			(1.6	)
Goodwill allocated to assets held for sale		—			(0.2	)		—			(0.2	)
Divestitures		—			—			(0.5	)		(0.5	)
Balance at end of period	$	430.9		$	143.4		$	1,822.5		$	2,396.8

	2018
Balance at beginning of period	$	281.4		$	50.3		$	1,828.6		$	2,160.3
Acquisitions		150.5			94.8			—			245.3
Goodwill allocated to assets held for sale		—			—			(5.6	)		(5.6	)
Divestitures		—			(0.9	)		—			(0.9	)
Balance at end of period	$	431.9		$	144.2		$	1,823.0		$	2,399.1

Intangible assets subject to amortization consist of the following:

December 31	Gross Amount		Accumulated Amortization			Net Balance
(in millions)	2019
Noncompetition agreements	$	6.3	$	(6.2	)	$	0.1
Customer relationships		65.6		(30.4	)		35.2
Operating permits		459.0		(42.3	)		416.7
Use rights and other		16.7		(12.1	)		4.6
Trade names		12.8		(10.9	)		1.9
Total	$	560.4	$	(101.9	)	$	458.5

	2018
Noncompetition agreements	$	6.3	$	(6.2	)	$	0.1
Customer relationships		65.6		(25.6	)		40.0
Operating permits		459.0		(36.1	)		422.9
Use rights and other		16.7		(11.2	)		5.5
Trade names		12.8		(9.7	)		3.1
Total	$	560.4	$	(88.8	)	$	471.6

Intangible assets deemed to have an indefinite life that are therefore not amortized consist of the following:

December 31	Building Materials Business		Magnesia Specialties		Total
(in millions)	2019
Operating permits	$	6.6	$	—	$	6.6
Use rights		19.0		—		19.0
Trade names		0.2		2.5		2.7
Total	$	25.8	$	2.5	$	28.3

	2018
Operating permits	$	6.6	$	—	$	6.6
Use rights		20.3		—		20.3
Trade names		0.3		2.5		2.8
Total	$	27.2	$	2.5	$	29.7

During 2019, the Company acquired $1.5 million of intangible assets, consisting of use rights not subject to amortization.

Total amortization expense for intangible assets for the years ended December 31, 2019, 2018 and 2017 was $13.0 million, $13.9 million and $14.2 million, respectively.

The estimated amortization expense for intangible assets for each of the next five years and thereafter is as follows:

(in millions)
2020	$	13.2
2021		12.5
2022		11.1
2023		10.6
2024		10.6
Thereafter		400.5
Total	$	458.5

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Changes in Asset Retirement Obligations

The following shows the changes in the asset retirement obligations:

years ended December 31 (in millions)	2019			2018
Balance at beginning of year	$	121.8		$	109.7
Accretion expense		5.6			5.1
Liabilities incurred and liabilities assumed in business combinations		0.6			4.6
Liabilities settled		(1.2	)		(2.8	)
Revisions in estimated cash flows		17.1			5.2
Balance at end of year	$	143.9		$	121.8

Schedule of Contractual Purchase Commitments

The Company’s contractual purchase commitments as of December 31, 2019 are as follows:

(in millions)
2020	$	140.6
2021		15.0
2022		3.0
2023		0.9
2024		0.9
Thereafter		15.9
Total	$	176.3

Schedule of Future Minimum Contracts of Affreightment and Royalty Commitments for All Noncancelable Agreements

Future minimum contracts of affreightment and royalty commitments for all noncancelable agreements as of December 31, 2019 are as follows:

(in millions)	Contracts of Affreightment		Royalty Commitments
2020	$	15.8	$	15.7
2021		16.1		11.1
2022		16.3		10.3
2023		16.6		9.2
2024		16.9		8.9
Thereafter		52.2		59.7
Total	$	133.9	$	114.9

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Target Assets Allocation (Detail)	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	100.00%
Total	100.00%	100.00%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	56.00%
Total	64.00%	57.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	30.00%
Total	28.00%	32.00%
Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	4.00%
Total	3.00%	6.00%
Real Estate
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	10.00%
Total	5.00%	5.00%

Long-Term Debt - Schedule of Corporation's Long-Term Debt Maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
2020	$ 340.0
2021	0.1
2022	0.1
2024	696.7
Thereafter	1,736.7
Total	$ 2,773.6	$ 3,120.4

Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Amounts Recognized on Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Current pension and postretirement benefits	$ (6.4)	$ (9.0)
Noncurrent pension, postretirement and postemployment benefits	(103.4)	(121.0)
Net amount recognized at end of year	(109.8)	(130.0)
Current pension and postretirement benefits	(2.0)	(1.0)
Noncurrent pension, postretirement and postemployment benefits	(11.0)	(12.3)
Net amount recognized at end of year	$ (13.0)	$ (13.3)

Supplemental Cash Flow Information - Schedule Of Noncash Investing and Financing Activities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Accrued liabilities for purchases of property, plant and equipment	$ 54.2	$ 67.0	$ 61.6
Acquisition of assets through asset exchange	2.4		2.5
Remeasurement of operating lease right-of-use assets	2.0
Right-of-use assets obtained in exchange for new operating lease liabilities	45.7
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 0.2
Acquisition of assets through capital lease		$ 1.1	0.8
Sale of asset to settle liability			$ 0.9

Long-Term Debt - Long-Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Maturity year	2024
Interest rate on notes	4.25%
Interest rate	4.25%
7% Debentures, Due 2025
Debt Instrument [Line Items]
Maturity year	2025
Interest rate on notes	7.00%
Interest rate	7.12%
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Maturity year	2027
Interest rate on notes	3.45%
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Maturity year	2027
Interest rate on notes	3.50%
Interest rate	3.53%
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Maturity year	2037
Interest rate on notes	6.25%
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Maturity year	2047
Interest rate on notes	4.25%
Interest rate	4.27%
Floating Rate Senior Notes, Due 2020
Debt Instrument [Line Items]
Maturity year	2020
Interest rate	2.55%	3.30%
Floating Rate Senior Notes, Due 2019
Debt Instrument [Line Items]
Maturity year	2019
Interest rate		3.29%
Trade Receivable Facility
Debt Instrument [Line Items]
Credit Facility interest rate	2.42%	3.07%