SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Net periodic (benefit) expense:
Interest cost	$ 3,285	$ 4,075	$ 9,569	$ 12,602
Expected return on plan assets	(5,887)	(4,815)	(17,149)	(14,893)
Amortization of actuarial loss	748	617	2,179	1,909
Net periodic (benefit) expense	$ (1,854)	$ (123)	$ (5,401)	$ (382)