DEBT - Summary of Activity for Deferred Financing Fees (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization [Roll Forward]
Beginning balance	$ 15,475	$ 19,033
Loan origination fees	6,312	550
Amortization	(2,668)	(3,074)
Write off of deferred financing fees	(2,851)
Ending balance	16,268	16,509
Summit Materials, LLC
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization [Roll Forward]
Beginning balance	15,475	19,033
Loan origination fees	6,312	550
Amortization	(2,668)	(3,074)
Write off of deferred financing fees	(2,851)
Ending balance	$ 16,268	$ 16,509