STOCKHOLDERS' EQUITY (Schedule of Changes in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 25, 2016	Dec. 27, 2015	Dec. 28, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	$ 1,261,810	$ 2,196,801	$ 1,492,602
Amounts reclassified from accumulated other comprehensive loss to net income	67	133
Total other comprehensive income (loss)	(5,313)	3,611	(16,806)
Balance, end of year	896,747	1,261,810	2,196,801
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	(58,930)	(62,541)	(45,735)
Other comprehensive income (loss) before reclassifications	(5,247)	3,744
Amounts reclassified from accumulated other comprehensive loss to net income	(66)	(133)
Total other comprehensive income (loss)	(5,313)	3,611	(16,806)
Balance, end of year	(64,243)	(58,930)	(62,541)
Losses Related to Pension and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	(58,997)	(62,572)
Other comprehensive income (loss) before reclassifications	(4,836)	4,004
Amounts reclassified from accumulated other comprehensive loss to net income	(410)	(429)
Total other comprehensive income (loss)	(5,246)	3,575
Balance, end of year	(64,243)	(58,997)	(62,572)
Unrealized Holding Gains on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	67	31
Other comprehensive income (loss) before reclassifications	(411)	(260)
Amounts reclassified from accumulated other comprehensive loss to net income	344	296
Total other comprehensive income (loss)	(67)	36
Balance, end of year	$ 0	$ 67	$ 31