STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 588,728	$ 560,883	$ 520,461	$ 458,999
Impact on unrecognized net actuarial gain (loss)
Change in the unrecognized net actuarial gain (loss), after tax	(7,535)	(13,567)	18,683
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(38,507)	(31,932)	(17,907)
Total after-tax amount	(27,496)	(23,479)	(14,912)	$ (57,372)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(35,231)	(30,140)	(17,044)
Total after-tax amount	(25,497)	(22,387)	(14,386)
Interest Rate Swap
Accumulated Other Comprehensive Loss
Total pre-tax amount	(897)	(576)
Total after-tax amount	(545)	(350)
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(2,379)	(1,216)	(863)
Total after-tax amount	(1,454)	(742)	$ (526)
Nonunion Defined Benefit Pension Plan
Impact on unrecognized net actuarial gain (loss)
Change in the unrecognized net actuarial gain (loss), pre-tax	(4,200)	(8,300)
Change in the unrecognized net actuarial gain (loss), after tax	$ (2,500)	(5,100)
Postretirement Health Benefit Plan
Impact on unrecognized net actuarial gain (loss)
Change in the unrecognized net actuarial gain (loss), pre-tax		(5,200)
Change in the unrecognized net actuarial gain (loss), after tax		$ (3,200)