Significant Accounting Policies - Comprehensive Earnings Attributable to Martin Marietta Materials Incorporated (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net earnings attributable to Martin Marietta Materials, Inc.	$ 25.9	$ 42.9
Other comprehensive earnings, net of tax	0.4	3.2
Earnings attributable to Martin Marietta Materials, Inc.	$ 26.3	$ 46.1

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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