STOCKHOLDERS' EQUITY (Schedule of Changes in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 27, 2015	Dec. 28, 2014
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning of year	$ (62,541)	$ (45,735)
Other comprehensive income (loss) before reclassifications	3,744	(16,491)
Amounts reclassified from accumulated other comprehensive loss to net income	(133)	(315)
Net current year other comprehensive income (loss)	3,611	(16,806)
Balance, end of year	(58,930)	(62,541)
Losses Related to Pension and Other Postretirement Benefits [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning of year	(62,572)	(45,797)
Other comprehensive income (loss) before reclassifications	4,004	(16,810)
Amounts reclassified from accumulated other comprehensive loss to net income	(429)	35
Net current year other comprehensive income (loss)	3,575	(16,775)
Balance, end of year	(58,997)	(62,572)
Unrealized Holding Gains on Available-for-Sale Securities [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning of year	31	62
Other comprehensive income (loss) before reclassifications	(260)	319
Amounts reclassified from accumulated other comprehensive loss to net income	296	(350)
Net current year other comprehensive income (loss)	36	(31)
Balance, end of year	$ 67	$ 31