SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020
Net periodic (benefit) expense:
Interest cost	$ 2,479	$ 3,285	$ 7,508	$ 9,569
Expected return on plan assets	(6,957)	(5,887)	(21,061)	(17,149)
Amortization of actuarial loss	827	748	2,502	2,179
Net periodic (benefit) expense	$ (3,651)	$ (1,854)	$ (11,051)	$ (5,401)