DEBT - Summary of Activity for Deferred Financing Fees (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization [Roll Forward]
Beginning balance	$ 15,436	$ 15,475
Loan origination fees		5,774
Amortization	(833)	(998)
Write off of deferred financing fees		(2,851)
Ending balance	14,603	17,400
Summit Materials, LLC
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization [Roll Forward]
Beginning balance	15,436	15,475
Loan origination fees		5,774
Amortization	(833)	(998)
Write off of deferred financing fees		(2,851)
Ending balance	$ 14,603	$ 17,400