OTHER NON-OPERATING EXPENSE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Interest income	$ 725	$ 536	$ 590
Foreign currency exchange (loss) / gain, net	(2,691)	17,761	6,929
Change in fair value of derivatives (Note 14)	(1,715)	(1,783)	(10,213)
Other income, net	508	428	442
Total other non-operating (expense) / income, net	$ (3,173)	$ 16,942	$ (2,252)