Significant Accounting Policies - Basic and Diluted Earnings from Continuing Operations Per Common Share (Detail) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Net earnings from continuing operations attributable to Martin Marietta	$ 353,200,000	$ 225.8	$ 377,700,000	$ 291.1
Less: Distributed and undistributed earnings attributable to unvested awards		0.2		0.2
Basic and diluted net earnings from continuing operations available to common shareholders attributable to Martin Marietta	$ 353,200,000	$ 225.6	$ 377,700,000	$ 290.9
Basic weighted-average common shares outstanding	62.4	62.4	62.4	62.4
Effect of dilutive employee and director awards	0.1	0.1	0.2	0.1
Diluted weighted-average common shares outstanding	62.5	62.5	62.6	62.5