PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Defined Benefit Plan Obligations and Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2016	Mar. 29, 2015	Dec. 27, 2015	Dec. 28, 2014
Change in plan assets:
Fair value of plan assets, beginning of period	$ 96,947
Fair value of plan assets, end of period	91,677
Pension Benefits [Member]
Change in projected benefit obligation:
Projected benefit obligation, beginning of period	165,952	$ 190,401
Interest cost	1,396	1,938
Actuarial losses	4,417	6,915
Benefits paid	(2,365)	(1,479)
Curtailments and settlements	0	(11,945)
Projected benefit obligation, end of period	169,400	185,830
Change in plan assets:
Fair value of plan assets, beginning of period	96,947	113,552
Actual return on plan assets	(5,446)	2,061
Contributions by employer	2,541	1,881
Benefits paid	(2,365)	(1,479)
Curtailments and settlements	0	(11,945)
Fair value of plan assets, end of period	91,677	104,070
Funded status:
Unfunded benefit obligation, end of period	(77,723)		$ (69,005)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(10,774)		(10,779)
Long-term liability	(66,949)		(58,226)
Recognized liability	(77,723)		(69,005)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	49,126	47,191	38,115	$ 43,907
Other Benefits [Member]
Change in projected benefit obligation:
Projected benefit obligation, beginning of period	1,672	1,657
Interest cost	12	17
Actuarial losses	51	38
Benefits paid	(35)	(32)
Curtailments and settlements	0	0
Projected benefit obligation, end of period	1,700	1,680
Change in plan assets:
Fair value of plan assets, beginning of period	0	0
Actual return on plan assets	0	0
Contributions by employer	35	32
Benefits paid	(35)	(32)
Curtailments and settlements	0	0
Fair value of plan assets, end of period	0	0
Funded status:
Unfunded benefit obligation, end of period	(1,700)		(1,672)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(139)		(138)
Long-term liability	(1,561)		(1,534)
Recognized liability	(1,700)		(1,672)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	$ (28)	$ (88)	$ (79)	$ (127)