ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of accumulated other comprehensive loss [Roll Forward]
Balance	$ 616,881
Other comprehensive income	1,376	$ 551
Balance	639,890
AOCI Attributable to Parent [Member]
Components of accumulated other comprehensive loss [Roll Forward]
Balance	(1,642)
Balance	(266)
Foreign Currency Translation Adjustment [Member]
Components of accumulated other comprehensive loss [Roll Forward]
Balance	(1,303)
Other comprehensive income	1,363
Balance	60
Postretirement Benefit Plan [Member]
Components of accumulated other comprehensive loss [Roll Forward]
Balance	(339)
Other comprehensive income	13
Balance	$ (326)