REVENUE RECOGNITION - By Product (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Revenue from External Customer [Line Items]
Total revenue	$ 732,082	$ 694,661	$ 1,665,612	$ 1,609,972
Aggregates
Revenue from External Customer [Line Items]
Total revenue	137,528	109,621	354,050	280,761
Cement
Revenue from External Customer [Line Items]
Total revenue	92,482	87,909	202,780	197,439
Ready-mix concrete
Revenue from External Customer [Line Items]
Total revenue	172,758	164,866	444,258	447,490
Asphalt
Revenue from External Customer [Line Items]
Total revenue	137,753	125,153	254,156	231,666
Paving and related services
Revenue from External Customer [Line Items]
Total revenue	138,083	146,477	267,732	288,119
Other
Revenue from External Customer [Line Items]
Total revenue	53,478	60,635	142,636	164,497
Summit Materials, LLC
Revenue from External Customer [Line Items]
Total revenue	732,082	694,661	1,665,612	1,609,972
Summit Materials, LLC | Aggregates
Revenue from External Customer [Line Items]
Total revenue	137,528	109,621	354,050	280,761
Summit Materials, LLC | Cement
Revenue from External Customer [Line Items]
Total revenue	92,482	87,909	202,780	197,439
Summit Materials, LLC | Ready-mix concrete
Revenue from External Customer [Line Items]
Total revenue	172,758	164,866	444,258	447,490
Summit Materials, LLC | Asphalt
Revenue from External Customer [Line Items]
Total revenue	137,753	125,153	254,156	231,666
Summit Materials, LLC | Paving and related services
Revenue from External Customer [Line Items]
Total revenue	138,083	146,477	267,732	288,119
Summit Materials, LLC | Other
Revenue from External Customer [Line Items]
Total revenue	$ 53,478	$ 60,635	$ 142,636	$ 164,497