Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Effective change in income tax rate	21.00%	18.80%
Discrete benefit from change in tax status of subsidiary from partnership to corporation	$ 6.9	$ 13.2

Effective income tax percentage reconciliation change in reclassification from partnership to corporation.

No definition available.

Name:	mlm_EffectiveIncomeTaxPercentageReconciliationChangeInReclassificationFromPartnershipToCorporation
Namespace Prefix:	mlm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration