Significant Accounting Policies - Basic and Diluted Earnings from Continuing Operations Per Common Share (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net earnings from continuing operations attributable to Martin Marietta	$ 24.5	$ 65.3
Less: Distributed and undistributed earnings attributable to unvested awards		0.1
Basic and diluted net earnings from continuing operations available to common shareholders attributable to Martin Marietta	$ 24.5	$ 65.2
Basic weighted-average common shares outstanding	62.4	62.3
Effect of dilutive employee and director awards	0.2	0.2
Diluted weighted-average common shares outstanding	62.6	62.5