Employee Benefit Plans - Multiemployer Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019
Multiemployer Plans [Line Items]
Contributions of Company	$ 120	$ 135
Construction Industry Laborers Pension Fund
Multiemployer Plans [Line Items]
Contributions of Company	100	112
Operating Engineers Local 101 Pension Plan
Multiemployer Plans [Line Items]
Contributions of Company	20	23
Summit Materials, LLC
Multiemployer Plans [Line Items]
Contributions of Company	120	135
Summit Materials, LLC | Construction Industry Laborers Pension Fund
Multiemployer Plans [Line Items]
Contributions of Company	100	112
Summit Materials, LLC | Operating Engineers Local 101 Pension Plan
Multiemployer Plans [Line Items]
Contributions of Company	$ 20	$ 23