EARNINGS PER SHARE - Schedule of Basic to Diluted Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2021	Sep. 26, 2020	Oct. 02, 2021	Sep. 26, 2020
Reconciliation of basic to diluted loss per share
Net income attributable to Summit Inc.	$ 74,204	$ 90,730	$ 108,346	$ 102,815
Diluted net income attributable to Summit Inc.	$ 74,204	$ 90,730	$ 108,346	$ 102,815
LP Units
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share (in shares)	1,594,272	3,053,115	2,031,090	3,086,819
Add: stock options
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share (in shares)	0	2,095,929	0	2,095,929
Warrants
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share (in shares)	0	100,037	0	100,037
Time-vesting restricted stock units
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share (in shares)	0	0	0	0
Market-based restricted stock units
Reconciliation of basic to diluted loss per share
Anti dilutive shares excluded from calculation of earnings per share (in shares)	0	0	0	0
Restricted Stock
Reconciliation of basic to diluted loss per share
Add: Nonvested restricted stock awards of retirement eligible shares (in shares)	200,575	320,343	218,224	145,155
Common Class A
Reconciliation of basic to diluted loss per share
Weighted average shares of Class A stock outstanding (in shares)	118,272,955	114,116,564	117,040,207	113,943,292
Weighted average basic shares outstanding (in shares)	118,272,955	114,116,564	117,040,207	113,943,292
Basic (usd per share)	$ 0.63	$ 0.79	$ 0.92	$ 0.90
Add: warrants (in shares)	14,405	0	17,573	0
Weighted average dilutive shares outstanding (in shares)	119,291,646	114,472,171	118,360,615	114,457,276
Diluted earnings (loss) per share (usd per share)	$ 0.62	$ 0.79	$ 0.92	$ 0.90
Common Class A | Add: stock options
Reconciliation of basic to diluted loss per share
Add: share-based payment arrangements (in shares)	125,164	0	310,990	0
Common Class A | Add: restricted stock units
Reconciliation of basic to diluted loss per share
Add: share-based payment arrangements (in shares)	680,980	263,886	812,702	450,353
Common Class A | Add: performance stock units
Reconciliation of basic to diluted loss per share
Add: share-based payment arrangements (in shares)	198,142	91,721	179,143	63,631
Common Class A And Restricted Stock
Reconciliation of basic to diluted loss per share
Weighted average shares of Class A stock outstanding (in shares)	118,473,530	114,436,907	117,258,431	114,088,447
Weighted average basic shares outstanding (in shares)	118,473,530	114,436,907	117,258,431	114,088,447
Basic (usd per share)	$ 0.63	$ 0.79	$ 0.92	$ 0.90