Income Taxes - Components of Income Tax Benefit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Provision for income taxes:
Current	$ 3,827	$ 69	$ 463
Deferred	(16,012)	17,032	59,284
Income tax expense (benefit)	(12,185)	17,101	59,747
Summit Materials, LLC
Provision for income taxes:
Current	3,827	69	463
Deferred	(2,764)	6,316	9,810
Income tax expense (benefit)	$ 1,063	$ 6,385	$ 10,273