Significant Accounting Policies - Noncurrent Deferred Tax Assets Recorded in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Equity [Abstract]
Balance at beginning of period, Pension and Postretirement Benefit Plans	$ 85.2	$ 84.2
Tax effect of other comprehensive earnings, Pension and Postretirement Benefit Plans	(0.8)	(0.9)
Balance at end of period, Pension and Postretirement Benefit Plans	$ 84.4	$ 83.3

Accumulated other comprehensive loss, noncurrent deferred tax assets, other comprehensive earnings, tax effect, pension and postretirement benefit plans.

No definition available.

Name:	mlm_AccumulatedOtherComprehensiveLossNoncurrentDeferredTaxAssetsOtherComprehensiveEarningsTaxEffectPensionAndPostretirementBenefitPlans
Namespace Prefix:	mlm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration