PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2021	Jun. 27, 2020	Jun. 26, 2021	Jun. 27, 2020
Employee benefits
Service cost	$ 911	$ 798	$ 1,822	$ 1,595
Interest cost	1,344	2,354	2,688	4,709
Expected return on plan assets	(1,983)	(2,982)	(3,967)	(5,963)
Amortization of prior service cost (credit)	(128)	(126)	(256)	(251)
Amortization of net loss	1,110	1,586	2,220	3,172
Other adjustments	(572)	125	(572)	250
Net periodic cost	682	1,755	1,935	3,512
Other Postretirement Benefits Plan
Employee benefits
Net periodic cost	$ 0	$ 0	$ 0	$ 0