STOCKHOLDERS' EQUITY (AOCI comp) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in accumulated other comprehensive loss, net of tax, by component
Balances	$ 588,728	$ 560,883	$ 520,461
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	4,079	(4,017)	(8,567)
Balances	598,897	588,728	560,883
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive loss, net of tax, by component
Balances	(27,496)	(23,479)	(14,912)
Other comprehensive income (loss) before reclassifications	(799)	(8,442)
Amounts reclassified from accumulated other comprehensive loss	4,878	4,425
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	4,079	(4,017)	(8,567)
Balances	(23,417)	(27,496)	(23,479)
Unrecognized Net Periodic Benefit Costs
Changes in accumulated other comprehensive loss, net of tax, by component
Balances	(25,497)	(22,387)
Other comprehensive income (loss) before reclassifications	(1,267)	(7,535)
Amounts reclassified from accumulated other comprehensive loss	4,878	4,425
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	3,611	(3,110)
Balances	(21,886)	(25,497)	(22,387)
Interest Rate Swap
Changes in accumulated other comprehensive loss, net of tax, by component
Balances	(545)	(350)
Other comprehensive income (loss) before reclassifications	216	(195)
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	216	(195)
Balances	(329)	(545)	(350)
Foreign Currency Translation
Changes in accumulated other comprehensive loss, net of tax, by component
Balances	(1,454)	(742)
Other comprehensive income (loss) before reclassifications	252	(712)
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	252	(712)
Balances	$ (1,202)	$ (1,454)	$ (742)