Significant Accounting Policies - Comprehensive Earnings Attributable to Martin Marietta Materials Incorporated (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net earnings attributable to Martin Marietta Materials, Inc.	$ 248,573	$ 180,221	$ 480,901	$ 375,621
Other comprehensive earnings, net of tax	2,569	4,392	8,814	7,613
Earnings attributable to Martin Marietta Materials, Inc.	$ 251,142	$ 184,613	$ 489,715	$ 383,234