STOCKHOLDERS' EQUITY/MEMBERS' INTEREST - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	9 Months Ended
	Oct. 02, 2021	Sep. 26, 2020
Changes in each component of accumulated other comprehensive loss
Beginning balance	$ 1,616,268	$ 1,444,773
Foreign currency translation adjustment, net of tax	467	(2,473)
Ending balance	1,771,764	1,569,496
Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Foreign currency translation adjustment, net of tax	682	(3,395)
Change in retirement plans
Changes in each component of accumulated other comprehensive loss
Beginning balance	533	2,171
Ending balance	533	2,171
Change in retirement plans | Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	(8,546)	(6,317)
Ending balance	(8,546)	(6,317)
Foreign currency translation adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance	4,670	1,277
Foreign currency translation adjustment, net of tax	467	(2,473)
Ending balance	5,137	(1,196)
Foreign currency translation adjustments | Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	(10,037)	(14,654)
Foreign currency translation adjustment, net of tax	682	(3,395)
Ending balance	(9,355)	(18,049)
Cash flow hedge adjustments | Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	0	0
Ending balance	0	0
Accumulated other comprehensive income (loss)
Changes in each component of accumulated other comprehensive loss
Beginning balance	5,203	3,448
Ending balance	5,670	975
Accumulated other comprehensive income (loss) | Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	(18,583)	(20,971)
Ending balance	$ (17,901)	$ (24,366)