SEGMENT INFORMATION - Financial Data (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2021 USD ($)	Sep. 26, 2020 USD ($)	Oct. 02, 2021 USD ($) segment	Sep. 26, 2020 USD ($)	Jan. 02, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Number of reportable segments | segment			3
Total revenue	$ 717,240	$ 709,619	$ 1,813,001	$ 1,707,818
Income from operations before taxes	95,891	73,156	143,369	79,597
Interest expense	24,134	24,623	72,536	78,049
Depreciation, depletion and amortization	58,381	57,364	171,474	161,912
Accretion	701	690	2,177	1,848
Loss on debt financings	6,016	4,064	6,016	4,064
Loss (gain) on sale of businesses	113	0	(15,319)	0
Non-cash compensation	4,685	13,322	14,875	23,119
Other	363	4,083	682	4,287
Total Adjusted EBITDA	190,284	177,302	395,810	352,876
Total purchases of property, plant and equipment			170,070	140,006
Total depreciation, depletion, amortization and accretion	59,082	58,054	173,651	163,760
Total assets	4,216,649		4,216,649		$ 4,308,011
Operating segment
Segment Reporting Information [Line Items]
Total purchases of property, plant and equipment			169,458	138,251
Total depreciation, depletion, amortization and accretion	58,014	57,075	170,378	160,800
Total assets	3,749,757		3,749,757		3,657,959
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	(11,463)	(10,197)	(36,306)	(27,077)
Total purchases of property, plant and equipment			612	1,755
Total depreciation, depletion, amortization and accretion	1,068	979	3,273	2,960
Total assets	466,892		466,892		650,052
West
Segment Reporting Information [Line Items]
Total revenue	369,250	390,310	958,351	919,016
West | Operating segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	92,303	95,470	211,722	196,881
Total purchases of property, plant and equipment			85,137	51,148
Total depreciation, depletion, amortization and accretion	24,796	23,117	75,287	67,082
Total assets	1,569,240		1,569,240		1,503,382
East
Segment Reporting Information [Line Items]
Total revenue	255,490	234,435	635,659	590,341
East | Operating segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	69,084	56,943	138,113	119,900
Total purchases of property, plant and equipment			69,469	75,006
Total depreciation, depletion, amortization and accretion	22,809	22,803	66,306	65,293
Total assets	1,316,659		1,316,659		1,303,742
Cement
Segment Reporting Information [Line Items]
Total revenue	92,500	84,874	218,991	198,461
Cement | Operating segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	40,360	35,086	82,281	63,172
Total purchases of property, plant and equipment			14,852	12,097
Total depreciation, depletion, amortization and accretion	10,409	11,155	28,785	28,425
Total assets	863,858		$ 863,858		850,835
Summit Materials, LLC
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Number of reportable segments | segment			3
Total revenue	717,240	709,619	$ 1,813,001	1,707,818
Income from operations before taxes	95,891	73,218	143,431	79,839
Interest expense	24,134	24,561	72,474	77,807
Depreciation, depletion and amortization	58,381	57,364	171,474	161,912
Accretion	701	690	2,177	1,848
Loss on debt financings	6,016	4,064	6,016	4,064
Loss (gain) on sale of businesses	113	0	(15,319)	0
Non-cash compensation	4,685	13,322	14,875	23,119
Other	363	4,083	682	4,287
Total Adjusted EBITDA	190,284	177,302	395,810	352,876
Total purchases of property, plant and equipment			170,070	140,006
Total depreciation, depletion, amortization and accretion	59,082	58,054	173,651	163,760
Total assets	4,007,260		4,007,260		4,077,134
Summit Materials, LLC | Operating segment
Segment Reporting Information [Line Items]
Total purchases of property, plant and equipment			169,458	138,251
Total depreciation, depletion, amortization and accretion	58,014	57,075	170,378	160,800
Total assets	3,749,757		3,749,757		3,657,959
Summit Materials, LLC | Corporate, Non-Segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	(11,463)	(10,197)	(36,306)	(27,077)
Total purchases of property, plant and equipment			612	1,755
Total depreciation, depletion, amortization and accretion	1,068	979	3,273	2,960
Total assets	257,503		257,503		419,175
Summit Materials, LLC | West
Segment Reporting Information [Line Items]
Total revenue	369,250	390,310	958,351	919,016
Summit Materials, LLC | West | Operating segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	92,303	95,470	211,722	196,881
Total purchases of property, plant and equipment			85,137	51,148
Total depreciation, depletion, amortization and accretion	24,796	23,117	75,287	67,082
Total assets	1,569,240		1,569,240		1,503,382
Summit Materials, LLC | East
Segment Reporting Information [Line Items]
Total revenue	255,490	234,435	635,659	590,341
Summit Materials, LLC | East | Operating segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	69,084	56,943	138,113	119,900
Total purchases of property, plant and equipment			69,469	75,006
Total depreciation, depletion, amortization and accretion	22,809	22,803	66,306	65,293
Total assets	1,316,659		1,316,659		1,303,742
Summit Materials, LLC | Cement
Segment Reporting Information [Line Items]
Total revenue	92,500	84,874	218,991	198,461
Summit Materials, LLC | Cement | Operating segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	40,360	35,086	82,281	63,172
Total purchases of property, plant and equipment			14,852	12,097
Total depreciation, depletion, amortization and accretion	10,409	$ 11,155	28,785	$ 28,425
Total assets	$ 863,858		$ 863,858		$ 850,835