INCOME TAXES - Summary of Current and Deferred Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 0	$ (730)	$ (15)
State	118	123	155
Foreign	277	507	61
Total current income tax provision	395	(100)	201
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	262	353	329
Total deferred income tax provision	262	353	329
Provision for income taxes	$ 657	$ 253	$ 530