ACCUMULATED OTHER COMPREHENSIVE INCOME, Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of accumulated other comprehensive income/(loss) [Roll Forward]
Balance	$ 463,705	$ 391,898	$ 331,358
Other comprehensive (loss)/gain	(1,735)	(2,463)	(2,849)
Balance	521,033	463,705	391,898
AOCI Attributable to Parent [Member]
Components of accumulated other comprehensive income/(loss) [Roll Forward]
Balance	(5,114)	(2,651)	198
Balance	(6,849)	(5,114)	$ (2,651)
Foreign Currency Translation Adjustment [Member]
Components of accumulated other comprehensive income/(loss) [Roll Forward]
Balance	(5,317)
Other comprehensive (loss)/gain	(1,390)
Balance	(6,707)	(5,317)
Postretirement Benefit Plan [Member]
Components of accumulated other comprehensive income/(loss) [Roll Forward]
Balance	203
Other comprehensive (loss)/gain	(345)
Balance	$ (142)	$ 203