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Significant Accounting Policies - Noncurrent Deferred Tax Assets Recorded in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Equity [Abstract] |  |
Balance at beginning of period, Pension and Postretirement Benefit Plans | $ 89.4 | $ 85.2
Tax effect of other comprehensive earnings, Pension and Postretirement Benefit Plans | (0.7) | (0.8)
Balance at end of period, Pension and Postretirement Benefit Plans | $ 88.7 | $ 84.4

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- Definition Accumulated other comprehensive loss, noncurrent deferred tax assets, other comprehensive earnings, tax effect, pension and postretirement benefit plans. + References No definition available. + Details
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Namespace Prefix: | mlm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Accumulated other comprehensive loss, noncurrent deferred tax assets, pension and postretirement benefit plans. + References No definition available. + Details
Name: | mlm_AccumulatedOtherComprehensiveLossNoncurrentDeferredTaxAssetsPensionAndPostretirementBenefitPlans
Namespace Prefix: | mlm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_EquityAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration