STOCK-BASED COMPENSATION - SUMMARY OF STOCK-BASED COMPENSATION EXPENSES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	$ 1,365	$ 1,081	$ 2,094	$ 3,184
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	343	173	388	493
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	251	190	420	820
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	771	718	1,286	1,871
Standard and market condition-based stock options outstanding
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	298	122	553	316
RSUs and RSAs
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	1,056	938	1,518	2,826
Employee stock purchase plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation, total	$ 11	$ 21	$ 23	$ 42