INTANGIBLE ASSETS - Summary of Changes in Carrying Amount of Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Roll Forward]
Balance at beginning of period	$ 42,065	$ 48,622	$ 11,293
Business acquisitions & adjustments	0	0	55,438
Amortization expense	(6,715)	(11,049)	(15,789)
Impairment expense	(2,521)	0	0
Currency translation adjustments and other	(2,036)	4,492	(2,320)
Balance at end of the period	$ 30,793	$ 42,065	$ 48,622