Significant Accounting Policies - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net earnings attributable to Martin Marietta Materials, Inc.	$ 248,573	$ 180,221	$ 480,901	$ 375,621
Less: Distributed and undistributed earnings attributable to unvested awards	345	271	886	672
Basic and diluted net earnings available to common shareholders attributable to Martin Marietta Materials, Inc.	$ 248,228	$ 179,950	$ 480,015	$ 374,949
Basic weighted-average common shares outstanding	62,510	62,932	62,552	62,970
Effect of dilutive employee and director awards	169	235	173	254
Diluted weighted-average common shares outstanding	62,679	63,167	62,725	63,224