SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Net periodic (benefit) expense:
Interest cost	$ 4,345	$ 4,716
Expected return on plan assets	(5,135)	(6,114)
Amortization of actuarial loss	658	804
Net periodic expense (benefit)	$ (132)	$ (594)