ACQUISITIONS, DISPOSTIONS, GOODWILL AND INTANGIBLES - Intangible Assets By Type (Details) - USD ($) $ in Thousands	Oct. 02, 2021	Jan. 02, 2021
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 84,647	$ 59,716
Accumulated Amortization	(14,309)	(11,864)
Net Carrying Amount	70,338	47,852
Operating permits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	33,671	33,671
Accumulated Amortization	(2,206)	(1,207)
Net Carrying Amount	31,465	32,464
Mineral leases
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	19,927	19,225
Accumulated Amortization	(8,497)	(7,571)
Net Carrying Amount	11,430	11,654
Reserve rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	25,586	6,234
Accumulated Amortization	(3,123)	(2,504)
Net Carrying Amount	22,463	3,730
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,463	586
Accumulated Amortization	(483)	(582)
Net Carrying Amount	4,980	4
Summit Materials, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	84,647	59,716
Accumulated Amortization	(14,309)	(11,864)
Net Carrying Amount	70,338	47,852
Summit Materials, LLC | Operating permits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	33,671	33,671
Accumulated Amortization	(2,206)	(1,207)
Net Carrying Amount	31,465	32,464
Summit Materials, LLC | Mineral leases
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	19,927	19,225
Accumulated Amortization	(8,497)	(7,571)
Net Carrying Amount	11,430	11,654
Summit Materials, LLC | Reserve rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	25,586	6,234
Accumulated Amortization	(3,123)	(2,504)
Net Carrying Amount	22,463	3,730
Summit Materials, LLC | Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,463	586
Accumulated Amortization	(483)	(582)
Net Carrying Amount	$ 4,980	$ 4