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Significant Accounting Policies - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) shares in Thousands, $ in Thousands | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Earnings Per Share [Abstract] |  |
Net earnings attributable to Martin Marietta Materials, Inc. | $ 42,853 | $ 10,023
Less: Distributed and undistributed earnings attributable to unvested awards | 86 | 63
Basic and diluted net earnings available to common shareholders attributable to Martin Marietta Materials, Inc. | $ 42,767 | $ 9,960
Basic weighted-average common shares outstanding | 62,584 | 62,957
Effect of dilutive employee and director awards | 193 | 265
Diluted weighted-average common shares outstanding | 62,777 | 63,222

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