FAIR VALUE - Fair Value Measurements (Details) - Level 3 $ in Thousands	3 Months Ended
	Mar. 28, 2020 USD ($)	Mar. 30, 2019 USD ($)	Dec. 28, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current portion of acquisition-related liabilities and accrued expenses - contingent consideration	$ 525		$ 1,967
Acquisition-related liabilities and other noncurrent liabilities - contingent consideration	1,231		1,302
Adjustment to contingent consideration	0	$ 0
Summit Materials, LLC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current portion of acquisition-related liabilities and accrued expenses - contingent consideration	525		1,967
Acquisition-related liabilities and other noncurrent liabilities - contingent consideration	$ 1,231		$ 1,302
Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration fair value measurement input	0.100
Discount Rate | Summit Materials, LLC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration fair value measurement input	0.100