NOTES PAYABLE - Composition of Notes Payable (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Principal amount outstanding	$ 7,667	$ 10,000
Unamortized debt discount	(32)	(69)
Accreted final payment fee	669	367
Total note payable	8,304	10,298
Less: current maturities	(3,976)	(2,294)
Note payable, net of current portion	$ 4,328	$ 8,004