PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Defined Benefit Plan Obligations and Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 26, 2017	Mar. 27, 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	101,180
Pension Benefits
Change in projected benefit obligation:
Projected benefit obligation, beginning of period	167,159	$ 165,952
Interest cost	1,393	1,396
Actuarial losses (gains)	785	4,417
Benefits paid	(2,237)	(2,365)
Projected benefit obligation, end of period	167,100	169,400
Change in plan assets:
Fair value of plan assets, beginning of period	97,526	96,947
Actual return on plan assets	3,965	(5,446)
Contributions by employer	1,926	2,541
Benefits paid	(2,237)	(2,365)
Fair value of plan assets, end of period	101,180	91,677
Funded status:
Unfunded benefit obligation, end of period	(65,920)		$ (69,633)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(13,108)		(13,113)
Long-term liability	(52,812)		(56,520)
Recognized liability	(65,920)		(69,633)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	44,394	49,126	46,494	$ 38,115
Other Benefits
Change in projected benefit obligation:
Projected benefit obligation, beginning of period	1,648	1,672
Interest cost	13	12
Actuarial losses (gains)	(24)	51
Benefits paid	(37)	(35)
Projected benefit obligation, end of period	1,600	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	37	35
Benefits paid	(37)	(35)
Fair value of plan assets, end of period	0	0
Funded status:
Unfunded benefit obligation, end of period	(1,600)		(1,648)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(147)		(147)
Long-term liability	(1,453)		(1,501)
Recognized liability	(1,600)		(1,648)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	$ (55)	$ (28)	$ (31)	$ (79)