ACCRUED EXPENSES - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 28, 2019
Schedule Of Accrued Expenses [Line Items]
Interest	$ 11,413	$ 26,892
Payroll and benefits	37,862	29,356
Finance lease obligations	24,868	16,007
Insurance	16,888	14,968
Non-income taxes	18,949	7,666
Deferred asset purchase payments	9,686	3,525
Professional fees	788	902
Other	23,610	20,689
Accrued expenses	144,064	120,005
Summit Materials, LLC
Schedule Of Accrued Expenses [Line Items]
Interest	11,413	26,892
Payroll and benefits	37,862	29,356
Finance lease obligations	24,868	16,007
Insurance	16,888	14,968
Non-income taxes	19,180	7,898
Deferred asset purchase payments	9,686	3,525
Professional fees	788	902
Other	23,610	20,689
Accrued expenses	$ 144,295	$ 120,237