Significant Accounting Policies - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net earnings attributable to Martin Marietta Materials, Inc.	$ 189,475	$ 185,377	$ 232,328	$ 195,400
Less: Distributed and undistributed earnings attributable to unvested awards	400	317	491	378
Basic and diluted net earnings available to common shareholders attributable to Martin Marietta Materials, Inc.	$ 189,075	$ 185,060	$ 231,837	$ 195,022
Basic weighted-average common shares outstanding	62,563	63,021	62,574	62,989
Effect of dilutive employee and director awards	157	264	175	264
Diluted weighted-average common shares outstanding	62,720	63,285	62,749	63,253