GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Schedule of Condensed Consolidating Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2021	Sep. 26, 2020	Oct. 02, 2021	Sep. 26, 2020
Condensed Consolidating Statements of Operations
Revenue	$ 717,240	$ 709,619	$ 1,813,001	$ 1,707,818
Cost of revenue (excluding items shown separately below)	486,936	501,592	1,301,346	1,258,463
Depreciation, depletion, amortization and accretion	59,082	58,054	173,651	163,760
Operating (loss) income	125,017	100,617	195,881	158,957
Loss (gain) on sale of businesses	113	0	(15,319)	0
Income from operations before taxes	95,891	73,156	143,369	79,597
Income tax expense (benefit)	20,513	(19,613)	33,478	(25,333)
Net income (loss) attributable to Summit Inc/LLC	74,204	90,730	108,346	102,815
Comprehensive income attributable to member of Summit Materials, LLC	71,008	92,202	108,813	100,342
Summit Materials, LLC
Condensed Consolidating Statements of Operations
Revenue	717,240	709,619	1,813,001	1,707,818
Cost of revenue (excluding items shown separately below)	486,936	501,592	1,301,346	1,258,463
General and administrative expenses	46,205	49,356	142,123	126,638
Depreciation, depletion, amortization and accretion	59,082	58,054	173,651	163,760
Operating (loss) income	125,017	100,617	195,881	158,957
Other (income) loss, net	4,879	2,838	(4,705)	1,311
Interest expense (income)	24,134	24,561	72,474	77,807
Loss (gain) on sale of businesses	113	0	(15,319)	0
Income from operations before taxes	95,891	73,218	143,431	79,839
Income tax expense (benefit)	7,016	(5,106)	12,531	(4,877)
Net income (loss) attributable to Summit Inc/LLC	88,875	78,324	130,900	84,716
Comprehensive income attributable to member of Summit Materials, LLC	84,799	80,342	131,582	81,321
Summit Materials, LLC | Eliminations
Condensed Consolidating Statements of Operations
Revenue	(4,151)	(4,003)	(10,174)	(13,264)
Cost of revenue (excluding items shown separately below)	(4,151)	(4,003)	(10,174)	(13,264)
General and administrative expenses	0	0	0	0
Depreciation, depletion, amortization and accretion	0	0	0	0
Operating (loss) income	0	0	0	0
Other (income) loss, net	147,546	138,675	296,208	237,774
Interest expense (income)	0	0	0	0
Loss (gain) on sale of businesses	0		0
Income from operations before taxes	(147,546)	(138,675)	(296,208)	(237,774)
Income tax expense (benefit)	0	0	0	0
Net income (loss) attributable to Summit Inc/LLC	(147,546)	(138,675)	(296,208)	(237,774)
Comprehensive income attributable to member of Summit Materials, LLC	(151,622)	(136,657)	(295,526)	(241,169)
Issuers | Summit Materials, LLC | Reportable Legal Entities
Condensed Consolidating Statements of Operations
Revenue	0	0	0	0
Cost of revenue (excluding items shown separately below)	0	0	0	0
General and administrative expenses	16,372	23,955	51,555	50,964
Depreciation, depletion, amortization and accretion	1,068	980	3,273	2,960
Operating (loss) income	(17,440)	(24,935)	(54,828)	(53,924)
Other (income) loss, net	(141,753)	(134,672)	(290,566)	(235,001)
Interest expense (income)	35,033	31,170	102,981	95,379
Loss (gain) on sale of businesses	0		0
Income from operations before taxes	89,280	78,567	132,757	85,698
Income tax expense (benefit)	405	243	1,857	982
Net income (loss) attributable to Summit Inc/LLC	88,875	78,324	130,900	84,716
Comprehensive income attributable to member of Summit Materials, LLC	84,799	80,342	131,582	81,321
100% Owned Guarantors | Summit Materials, LLC | Reportable Legal Entities
Condensed Consolidating Statements of Operations
Revenue	686,736	689,842	1,735,193	1,659,526
Cost of revenue (excluding items shown separately below)	465,966	489,318	1,247,002	1,228,076
General and administrative expenses	28,373	23,952	87,968	71,282
Depreciation, depletion, amortization and accretion	55,081	55,542	161,783	156,697
Operating (loss) income	137,316	121,030	238,440	203,471
Other (income) loss, net	(1,044)	(889)	(9,784)	(1,733)
Interest expense (income)	(12,276)	(7,990)	(34,635)	(21,352)
Loss (gain) on sale of businesses	113		(15,319)
Income from operations before taxes	150,523	129,909	298,178	226,556
Income tax expense (benefit)	5,634	(6,286)	8,314	(7,383)
Net income (loss) attributable to Summit Inc/LLC	144,889	136,195	289,864	233,939
Comprehensive income attributable to member of Summit Materials, LLC	144,889	136,195	289,864	233,939
Non-Guarantors | Summit Materials, LLC | Reportable Legal Entities
Condensed Consolidating Statements of Operations
Revenue	34,655	23,780	87,982	61,556
Cost of revenue (excluding items shown separately below)	25,121	16,277	64,518	43,651
General and administrative expenses	1,460	1,449	2,600	4,392
Depreciation, depletion, amortization and accretion	2,933	1,532	8,595	4,103
Operating (loss) income	5,141	4,522	12,269	9,410
Other (income) loss, net	130	(276)	(563)	271
Interest expense (income)	1,377	1,381	4,128	3,780
Loss (gain) on sale of businesses	0		0
Income from operations before taxes	3,634	3,417	8,704	5,359
Income tax expense (benefit)	977	937	2,360	1,524
Net income (loss) attributable to Summit Inc/LLC	2,657	2,480	6,344	3,835
Comprehensive income attributable to member of Summit Materials, LLC	$ 6,733	$ 462	$ 5,662	$ 7,230