ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 691,618	$ 616,881
Other comprehensive (loss)/income	(1,084)	1,376
Ending balance	710,509	639,890
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,602)	(1,642)
Other comprehensive (loss)/income	(1,084)	1,376
Ending balance	(4,686)	$ (266)
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,285)
Other comprehensive (loss)/income	(1,089)
Ending balance	(5,374)
Postretirement benefit plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	683
Other comprehensive (loss)/income	5
Ending balance	$ 688