STOCKHOLDERS' EQUITY (AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Loss
Total after-tax amount	$ 598,897	$ 588,728	$ 560,883	$ 520,461
Impact on unrecognized net actuarial loss
Change in the unrecognized net actuarial loss, after tax	(1,267)	(7,535)	(13,567)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Loss
Total pre-tax amount	(31,840)	(38,507)	(31,932)
Total after-tax amount	(23,417)	(27,496)	(23,479)	$ (14,912)
Unrecognized Net Periodic Benefit Costs
Accumulated Other Comprehensive Loss
Total pre-tax amount	(29,320)	(35,231)	(30,140)
Total after-tax amount	(21,886)	(25,497)	(22,387)
Interest Rate Swap
Accumulated Other Comprehensive Loss
Total pre-tax amount	(542)	(897)	(576)
Total after-tax amount	(329)	(545)	(350)
Foreign Currency Translation
Accumulated Other Comprehensive Loss
Total pre-tax amount	(1,978)	(2,379)	(1,216)
Total after-tax amount	(1,202)	(1,454)	$ (742)
Nonunion Defined Benefit Pension Plan
Impact on unrecognized net actuarial loss
Change in the unrecognized net actuarial gain (loss), pre-tax	(5,200)	(4,200)
Change in the unrecognized net actuarial loss, after tax	$ (3,200)	$ (2,500)