STOCKHOLDERS' EQUITY (AOCI comp) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in accumulated other comprehensive loss, net of tax, by component
Balances			$ 599,055
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	$ (175)	$ 2,404	1,216	$ (943)
Balances	613,565		613,565
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive loss, net of tax, by component
Balances			(23,417)	(27,496)
Other comprehensive income (loss) before reclassifications			(2,712)	(4,542)
Amounts reclassified from accumulated other comprehensive loss			3,928	3,599
OTHER COMPREHENSIVE INCOME (LOSS), net of tax			1,216	(943)
Balances	(22,201)	(28,439)	(22,201)	(28,439)
Unrecognized Net Periodic Benefit Costs
Changes in accumulated other comprehensive loss, net of tax, by component
Balances			(21,886)	(25,497)
Other comprehensive income (loss) before reclassifications			(3,158)	(4,141)
Amounts reclassified from accumulated other comprehensive loss			3,928	3,599
OTHER COMPREHENSIVE INCOME (LOSS), net of tax			770	(542)
Balances	(21,116)	(26,039)	(21,116)	(26,039)
Interest Rate Swap
Changes in accumulated other comprehensive loss, net of tax, by component
Balances			(329)	(545)
Other comprehensive income (loss) before reclassifications			241	(430)
OTHER COMPREHENSIVE INCOME (LOSS), net of tax			241	(430)
Balances	(88)	(975)	(88)	(975)
Foreign Currency Translation
Changes in accumulated other comprehensive loss, net of tax, by component
Balances			(1,202)	(1,454)
Other comprehensive income (loss) before reclassifications			205	29
OTHER COMPREHENSIVE INCOME (LOSS), net of tax			205	29
Balances	$ (997)	$ (1,425)	$ (997)	$ (1,425)