Acquisitions - Acquisitions by Region (Details) - acquistiion	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
West
Business Acquisition [Line Items]
Number of business acquisitions	2	5	6
East
Business Acquisition [Line Items]
Number of business acquisitions	0	7	8
Summit Materials, LLC | West
Business Acquisition [Line Items]
Number of business acquisitions	2	5	6
Summit Materials, LLC | East
Business Acquisition [Line Items]
Number of business acquisitions	0	7	8