Significant Accounting Policies - Comprehensive Earnings Attributable to Martin Marietta Materials Incorporated (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net earnings attributable to Martin Marietta Materials, Inc.	$ 180,221	$ 151,546	$ 375,621	$ 336,159
Other comprehensive earnings, net of tax	4,392	2,978	7,613	7,759
Earnings attributable to Martin Marietta Materials, Inc.	$ 184,613	$ 154,524	$ 383,234	$ 343,918