ACCUMULATED OTHER COMPREHENSIVE INCOME - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 743,667	$ 691,618	$ 616,881
Other comprehensive gain/(loss)	9,737	(1,962)	(1,960)
Ending balance	828,233	743,667	691,618
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,564)	(3,602)	(1,642)
Ending balance	4,173	(5,564)	$ (3,602)
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,176)
Other comprehensive gain/(loss)	12,829
Ending balance	7,653	(5,176)
Cash flow hedge
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,399)
Other comprehensive gain/(loss)	(2,285)
Ending balance	(3,684)	(1,399)
Postretirement benefit plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,011
Other comprehensive gain/(loss)	(807)
Ending balance	$ 204	$ 1,011