Earnings Per Share - Schedule of Basic to Diluted Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Reconciliation of basic to diluted loss per share
Net income attributable to Summit Inc.	$ 137,967	$ 59,066	$ 33,906
Diluted net income attributable to Summit Inc.	$ 137,967	$ 59,066	$ 33,906
LP Units
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share	3,060,248	3,372,706	3,512,669
Warrant
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share	100,037	0	0
Restricted Stock
Reconciliation of basic to diluted loss per share
Add: Nonvested restricted stock awards of retirement eligible shares (in shares)	212,443	0	0
Common Class A
Reconciliation of basic to diluted loss per share
Weighted average shares outstanding (in shares)	114,014,749	112,204,067	111,380,175
Basic (USD per share)	$ 1.21	$ 0.53	$ 0.30
Add: warrants	0	4,206	25,049
Weighted average dilutive shares outstanding (in shares)	114,631,768	112,684,718	112,316,646
Diluted (USD per share)	$ 1.20	$ 0.52	$ 0.30
Common Class A | Stock Options
Reconciliation of basic to diluted loss per share
Add: Share-based payment arrangements	3,390	87,290	282,329
Common Class A | Restricted stock
Reconciliation of basic to diluted loss per share
Add: Share-based payment arrangements	520,871	342,620	459,280
Common Class A | Performance Stock Units
Reconciliation of basic to diluted loss per share
Add: Share-based payment arrangements	92,758	46,535	169,813
Common Class A and Restricted Stock
Reconciliation of basic to diluted loss per share
Weighted average shares outstanding (in shares)	114,227,192	112,204,067	111,380,175
Basic (USD per share)	$ 1.21	$ 0.53	$ 0.30