Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Oct. 24, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol MLM  
Entity Central Index Key 0000916076  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company false  
Title of 12(b) Security Common Stock (Par Value $0.01)  
Security Exchange Name NYSE  
Entity File Number 1-12744  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Incorporation, State or Country Code NC  
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 NC  
Entity Address, Postal Zip Code 27607-3033  
City Area Code 919  
Local Phone Number 781-4550  
Document Quarterly Report true  
Document Transition Report false  
Entity Common Stock, Shares Outstanding   62,500,533