INCOME TAXES - Summary of Current and Deferred Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (730)	$ (15)	$ 0
State	123	155	152
Foreign	507	61	158
Total current income tax provision	(100)	201	310
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	353	329	(3,970)
Total deferred income tax provision	353	329	(3,970)
Provision (benefit) for income taxes	$ 253	$ 530	$ (3,660)