Accrued Mining and Landfill Reclamation - Narrative (Detail) - USD ($) $ in Millions	Jan. 02, 2021	Dec. 28, 2019
Asset Retirement Obligations [Line Items]
Anticipated costs	$ 112.8	$ 97.4
Accrued expenses
Asset Retirement Obligations [Line Items]
Asset retirement obligation, current	10.0	7.9
Summit Materials, LLC
Asset Retirement Obligations [Line Items]
Anticipated costs	112.8	97.4
Summit Materials, LLC \| Accrued expenses
Asset Retirement Obligations [Line Items]
Asset retirement obligation, current	$ 10.0	$ 7.9

Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant