SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Net periodic (benefit) expense:
Interest cost	$ 4,478	$ 6,659	$ 8,799	$ 13,042
Expected return on plan assets	(5,054)	(6,084)	(9,931)	(12,083)
Amortization of actuarial loss	736	0	1,446	0
Net periodic expense	$ 160	$ 575	$ 314	$ 959