ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in accumulated other comprehensive income (loss) [Abstract]
Net foreign currency translation adjustment	$ (2,911)	$ 2,697	$ (1,548)	$ 3,238
Net change in postretirement benefit plan (see Note 15 for further information)
Amortization of prior service cost	17	19	35	38
Amortization of gain	(1)	(4)	(2)	(8)
Total before tax	16	15	33	30
Tax	0	(4)	(4)	(9)
Net of tax	16	11	29	21
Other comprehensive (loss)/income	$ (2,895)	$ 2,708	$ (1,519)	$ 3,259