ACCRUED LIABILITIES - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued outsourced clinical trials and preclinical studies	$ 959		$ 2,259
Accrued employee compensation and related taxes	686		508
Operating lease liability	397	$ 400	0
Restructuring liability	377		1,515
Accrued legal fees and expenses	311		284
Accrued other professional service fees	105		254
Value of liability-classified stock purchase warrants	100		100
Deferred and accrued facility lease obligations	0		66
Other accrued liabilities	85		122
Total accrued liabilities	$ 3,020		$ 5,108
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent		us-gaap:AccruedLiabilitiesCurrent