Leases - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Operating Leased Assets [Line Items]
Royalty expense recorded in cost of revenue	$ 29.2	$ 24.3	$ 20.1
Summit Materials, LLC
Operating Leased Assets [Line Items]
Royalty expense recorded in cost of revenue	$ 29.2	$ 24.3	$ 20.1

Amount of expense related to royalty payments under a contractual arrangement such as payment for mineral and drilling rights and use of technology or intellectual property.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Name:	us-gaap_RoyaltyExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration