ACCRUED LIABILITIES - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued outsourced clinical trials and preclinical studies	$ 2,259	$ 1,129
Restructuring liability	1,515	0
Accrued employee compensation and related taxes	508	1,704
Accrued legal fees and expenses	284	376
Accrued other professional service fees	254	246
Value of liability-classified stock purchase warrants	100	82
Deferred and accrued facility lease obligations	66	124
Accrued equipment and lab materials	1	33
Other accrued liabilities	121	174
Total accrued liabilities	$ 5,108	$ 3,868