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DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 28, 2020	Dec. 28, 2019	Mar. 15, 2019	Jun. 01, 2017	Jul. 08, 2015
Debt Instrument [Line Items]
Total debt	$ 1,870,802	$ 1,872,273
Current portion of debt	7,942	7,942
Long-term Debt, Excluding Current Maturities	1,862,860	1,864,331
Gross amount	1,872,668
Debt discount	1,866
Term Loan, due 2024
Debt Instrument [Line Items]
Total debt	621,608	623,140
Gross amount	625,800	630,600
Debt discount	1,100	1,100
6 1/8% Senior Notes, due 2023
Debt Instrument [Line Items]
Total debt	649,194	649,133
Gross amount	650,000	650,000
Debt discount	$ 800	900
Debt instrument interest rate (as a percent)	6.125%
5 1/8% Senior Notes, due 2025
Debt Instrument [Line Items]
Total debt	$ 300,000	300,000
Debt instrument interest rate (as a percent)	5.125%
Summit Materials, LLC
Debt Instrument [Line Items]
Total debt	$ 1,870,802	1,872,273
Current portion of debt	7,942	7,942
Long-term Debt, Excluding Current Maturities	1,862,860	1,864,331
Gross amount	1,872,668
Debt discount	1,866
Summit Materials, LLC \| Term Loan, due 2024
Debt Instrument [Line Items]
Total debt	621,608	623,140
Gross amount	622,700	624,300
Debt discount	1,100	1,100
Summit Materials, LLC \| 6 1/8% Senior Notes, due 2023
Debt Instrument [Line Items]
Total debt	649,194	649,133
Gross amount	650,000	650,000
Debt discount	$ 800	900
Debt instrument interest rate (as a percent)	6.125%				6.125%
Summit Materials, LLC \| 5 1/8% Senior Notes, due 2025
Debt Instrument [Line Items]
Total debt	$ 300,000	300,000		$ 300,000
Debt instrument interest rate (as a percent)	5.125%			5.125%
Senior Notes \| 6 1/2% Senior Notes, due 2027
Debt Instrument [Line Items]
Total debt	$ 300,000	300,000
Debt instrument interest rate (as a percent)	6.50%
Senior Notes \| Summit Materials, LLC \| 6 1/2% Senior Notes, due 2027
Debt Instrument [Line Items]
Total debt	$ 300,000	$ 300,000	$ 300,000
Debt instrument interest rate (as a percent)	6.50%		6.50%