Acquisitions - Summary of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Business Acquisition [Line Items]
Goodwill	$ 1,201,291	$ 1,199,699	$ 1,192,028
Summit Materials, LLC
Business Acquisition [Line Items]
Goodwill	1,202,291	1,200,699	$ 1,193,028
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Financial assets	8,696	0
Inventories	2,856	52
Property, plant and equipment	130,042	3,542
Other assets	2,790	0
Financial liabilities	(4,469)	(36)
Other long-term liabilities	(16,069)	0
Net assets acquired	123,846	3,558
Goodwill	0	1,834
Purchase price	123,846	5,392
Other	(369)	0
Net cash paid for acquisitions	123,477	5,392
Series of Individually Immaterial Business Acquisitions | Summit Materials, LLC
Business Acquisition [Line Items]
Financial assets	8,696	0
Inventories	2,856	52
Property, plant and equipment	130,042	3,542
Other assets	2,790	0
Financial liabilities	(4,469)	(36)
Other long-term liabilities	(16,069)	0
Net assets acquired	123,846	3,558
Goodwill	0	1,834
Purchase price	123,846	5,392
Other	(369)	0
Net cash paid for acquisitions	$ 123,477	$ 5,392