SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Net periodic (benefit) expense:
Interest cost	$ 4,486	$ 4,478	$ 9,202	$ 8,799
Expected return on plan assets	(5,815)	(5,054)	(11,929)	(9,931)
Amortization of actuarial loss	764	736	1,568	1,446
Net periodic expense (benefit)	$ (565)	$ 160	$ (1,159)	$ 314