STOCKHOLDERS' EQUITY (Schedule of Changes in Unrealized Actuarial Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2015	Sep. 28, 2014	Sep. 27, 2015	Sep. 28, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of period			$ (62,541)	$ (45,735)
Other comprehensive income (loss) before reclassifications			(3,712)	(9,925)
Amounts reclassified from accumulated other comprehensive loss to net income			251	(155)
Total other comprehensive loss, net of tax	$ (10,164)	$ (636)	(3,461)	(10,080)
Balance, end of period	(66,002)	(55,815)	(66,002)	(55,815)
Losses Related to Pension and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of period			(62,572)	(45,797)
Other comprehensive income (loss) before reclassifications			(3,845)	(10,094)
Amounts reclassified from accumulated other comprehensive loss to net income			334	26
Total other comprehensive loss, net of tax			(3,511)	(10,068)
Balance, end of period	(66,083)	(55,865)	(66,083)	(55,865)
Unrealized Holding Gains on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of period			31	62
Other comprehensive income (loss) before reclassifications			133	169
Amounts reclassified from accumulated other comprehensive loss to net income			(83)	(181)
Total other comprehensive loss, net of tax			50	(12)
Balance, end of period	$ 81	$ 50	$ 81	$ 50