PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Defined Benefit Plan Obligations and Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2016	Jun. 28, 2015	Jun. 26, 2016	Jun. 28, 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	$ 97,862		97,862
Pension Benefits [Member]
Change in projected benefit obligation:
Projected benefit obligation, beginning of period			165,952	$ 190,401
Interest cost	1,397	$ 1,939	2,793	3,877
Actuarial losses			12,736	(7,033)
Benefits paid			(4,581)	(2,981)
Curtailments and settlements			0	(13,014)
Projected benefit obligation, end of period	176,900	171,250	176,900	171,250
Change in plan assets:
Fair value of plan assets, beginning of period			96,947	113,552
Actual return on plan assets			1,084	3,455
Contributions by employer			4,412	3,177
Benefits paid			(4,581)	(2,981)
Curtailments and settlements			0	(13,014)
Fair value of plan assets, end of period	97,862	104,189	97,862	104,189
Funded status:
Unfunded benefit obligation, end of period	(79,038)		(79,038)		$ (69,005)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(10,769)		(10,769)		(10,779)
Long-term liability	(68,269)		(68,269)		(58,226)
Recognized liability	(79,038)		(79,038)		(69,005)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	52,065	33,133	52,065	33,133	38,115	$ 43,907
Other Benefits [Member]
Change in projected benefit obligation:
Projected benefit obligation, beginning of period			1,672	1,657
Interest cost	14	17	26	34
Actuarial losses			72	(27)
Benefits paid			(70)	(64)
Curtailments and settlements			0	0
Projected benefit obligation, end of period	1,700	1,600	1,700	1,600
Change in plan assets:
Fair value of plan assets, beginning of period			0	0
Actual return on plan assets			0	0
Contributions by employer			70	64
Benefits paid			(70)	(64)
Curtailments and settlements			0	0
Fair value of plan assets, end of period	0	0	0	0
Funded status:
Unfunded benefit obligation, end of period	(1,700)		(1,700)		(1,672)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(139)		(139)		(138)
Long-term liability	(1,561)		(1,561)		(1,534)
Recognized liability	(1,700)		(1,700)		(1,672)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	$ (7)	$ (153)	$ (7)	$ (153)	$ (79)	$ (127)