PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Defined Benefit Plan Obligations and Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 25, 2017	Jun. 26, 2016	Jun. 25, 2017	Jun. 26, 2016	Dec. 25, 2016	Dec. 27, 2015
Change in plan assets:
Fair value of plan assets, beginning of period			$ 97,526
Fair value of plan assets, end of period	$ 104,740		104,740
Pension Benefits
Change in projected benefit obligation:
Projected benefit obligation, beginning of period			167,159	$ 165,952
Interest cost	1,393	$ 1,397	2,786	2,793
Actuarial losses (gains)			8,885	12,736
Benefits paid			(4,430)	(4,581)
Projected benefit obligation, end of period	174,400	176,900	174,400	176,900
Change in plan assets:
Fair value of plan assets, beginning of period			97,526	96,947
Actual return on plan assets			7,142	1,084
Contributions by employer			4,502	4,412
Benefits paid			(4,430)	(4,581)
Fair value of plan assets, end of period	104,740	97,862	104,740	97,862
Funded status:
Unfunded benefit obligation, end of period	(69,660)		(69,660)		$ (69,633)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(13,103)		(13,103)		(13,113)
Long-term liability	(56,557)		(56,557)		(56,520)
Recognized liability	(69,660)		(69,660)		(69,633)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	50,398	52,065	50,398	52,065	46,494	$ 38,115
Other Benefits
Change in projected benefit obligation:
Projected benefit obligation, beginning of period			1,648	1,672
Interest cost	12	14	25	26
Actuarial losses (gains)			101	72
Benefits paid			(74)	(70)
Projected benefit obligation, end of period	1,700	1,700	1,700	1,700
Change in plan assets:
Fair value of plan assets, beginning of period			0	0
Actual return on plan assets			0	0
Contributions by employer			74	70
Benefits paid			(74)	(70)
Fair value of plan assets, end of period	0	0	0	0
Funded status:
Unfunded benefit obligation, end of period	(1,700)		(1,700)		(1,648)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(147)		(147)		(147)
Long-term liability	(1,553)		(1,553)		(1,501)
Recognized liability	(1,700)		(1,700)		(1,648)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	$ 70	$ (7)	$ 70	$ (7)	$ (31)	$ (79)