Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Revenue:
Revenue	$ 2,332,451	$ 2,222,140	$ 2,101,002
Cost of revenue (excluding items shown separately below):
Cost of revenue	1,583,996	1,526,332	1,475,779
General and administrative expenses	309,531	275,813	270,402
Depreciation, depletion, amortization and accretion	221,320	217,102	204,910
Gain on sale of property, plant and equipment	(7,569)	(10,665)	(12,555)
Operating income	225,173	213,558	162,466
Interest expense	103,595	116,509	116,548
Loss on debt financings	4,064	14,565	149
Tax receivable agreement (benefit) expense	(7,559)	16,237	(22,684)
Gain on sale of business	0	0	(12,108)
Other income, net	(3,982)	(11,977)	(15,516)
Income from operations before taxes	129,055	78,224	96,077
Income tax expense (benefit)	(12,185)	17,101	59,747
Net income	141,240	61,123	36,330
Net income attributable to noncontrolling interest	3,273	2,057	2,424
Net income attributable to Summit Inc.	137,967	59,066	33,906
Summit Materials, LLC
Revenue:
Revenue	2,332,451	2,222,140	2,101,002
Cost of revenue (excluding items shown separately below):
Cost of revenue	1,583,996	1,526,332	1,475,779
General and administrative expenses	309,531	275,813	270,402
Depreciation, depletion, amortization and accretion	221,320	217,102	204,910
Gain on sale of property, plant and equipment	(7,569)	(10,665)	(12,555)
Operating income	225,173	213,558	162,466
Interest expense	103,291	115,988	115,831
Loss on debt financings	4,064	14,565	149
Gain on sale of business	0	0	(12,108)
Other income, net	(3,982)	(11,977)	(15,516)
Income from operations before taxes	121,800	94,982	74,110
Income tax expense (benefit)	1,063	6,385	10,273
Net income	120,737	88,597	63,837
Net income attributable to Summit Inc.	$ 120,737	$ 88,597	$ 63,837
Common Class A
Earnings per share of Class A common stock:
Basic (USD per share)	$ 1.21	$ 0.53	$ 0.30
Diluted (USD per share)	$ 1.20	$ 0.52	$ 0.30
Weighted average shares of Class A common stock:
Basic (in shares)	114,014,749	112,204,067	111,380,175
Diluted (in shares)	114,631,768	112,684,718	112,316,646
Common Class A and Restricted Stock
Earnings per share of Class A common stock:
Basic (USD per share)	$ 1.21	$ 0.53	$ 0.30
Weighted average shares of Class A common stock:
Basic (in shares)	114,227,192	112,204,067	111,380,175
Product
Revenue:
Revenue	$ 1,824,679	$ 1,724,462	$ 1,600,159
Cost of revenue (excluding items shown separately below):
Cost of revenue	1,166,266	1,116,662	1,058,544
Product | Summit Materials, LLC
Revenue:
Revenue	1,824,679	1,724,462	1,600,159
Cost of revenue (excluding items shown separately below):
Cost of revenue	1,166,266	1,116,662	1,058,544
Service
Revenue:
Revenue	310,075	306,185	309,099
Cost of revenue (excluding items shown separately below):
Cost of revenue	220,033	218,177	225,491
Service | Summit Materials, LLC
Revenue:
Revenue	310,075	306,185	309,099
Cost of revenue (excluding items shown separately below):
Cost of revenue	220,033	218,177	225,491
Excluding delivery and subcontract revenue
Revenue:
Revenue	2,134,754	2,030,647	1,909,258
Cost of revenue (excluding items shown separately below):
Cost of revenue	1,386,299	1,334,839	1,284,035
Excluding delivery and subcontract revenue | Summit Materials, LLC
Revenue:
Revenue	2,134,754	2,030,647	1,909,258
Cost of revenue (excluding items shown separately below):
Cost of revenue	1,386,299	1,334,839	1,284,035
Delivery and subcontract revenue
Revenue:
Revenue	197,697	191,493	191,744
Cost of revenue (excluding items shown separately below):
Cost of revenue	197,697	191,493	191,744
Delivery and subcontract revenue | Summit Materials, LLC
Revenue:
Revenue	197,697	191,493	191,744
Cost of revenue (excluding items shown separately below):
Cost of revenue	$ 197,697	$ 191,493	$ 191,744