REVENUE RECOGNITION - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018
Change in Contract with Customer, Asset [Abstract]
Beginning balance	$ 18,602
Changes in revenue billed, contract price or cost estimates	31,085	$ 37,643
Other	28
Ending balance	49,715
Change in Contract with Customer, Liability [Abstract]
Beginning balance	11,840
Changes in revenue billed, contract price or cost estimates	618	(3,850)
Other	18
Ending balance	12,476
Summit Materials, LLC
Change in Contract with Customer, Asset [Abstract]
Beginning balance	18,602
Changes in revenue billed, contract price or cost estimates	31,085	37,643
Other	28
Ending balance	49,715
Change in Contract with Customer, Liability [Abstract]
Beginning balance	11,840
Changes in revenue billed, contract price or cost estimates	618	$ (3,850)
Other	18
Ending balance	$ 12,476