Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedule of Earnings Per Share, Basic and Diluted, by Common Class
Net earnings from continuing operations attributable to Martin Marietta Materials, Inc.	$ 63,040	$ 49,160	$ 63,335	$ 69,953
Less: Distributed and undistributed earnings attributable to unvested awards	336	378	386	557
Basic and diluted net earnings available to common shareholders from continuing operations attributable to Martin Marietta Materials, Inc.	62,704	48,782	62,949	69,396
Basic and diluted net loss available to common shareholders from discontinued operations	(118)	(4)	(395)	(2,412)
Basic and diluted net earnings available to common shareholders attributable to Martin Marietta Materials, Inc.	$ 62,586	$ 48,778	$ 62,554	$ 66,984
Basic weighted-average common shares outstanding	45,860	45,690	45,792	45,634
Effect of dilutive employee and director awards	132	109	137	149
Diluted weighted-average common shares outstanding	45,992	45,799	45,929	45,783