ACCRUED LIABILITIES - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued outsourced clinical trials and preclinical studies	$ 1,012		$ 2,259
Accrued employee compensation and related taxes	524		508
Restructuring liability	416		1,515
Accrued legal fees and expenses	323		284
Operating lease liability	306	$ 400
Accrued other professional service fees	282		254
Value of liability-classified stock purchase warrants	100		100
Deferred and accrued facility lease obligations	0		66
Accrued equipment and lab materials	11		1
Other accrued liabilities	81		121
Total accrued liabilities	$ 3,055		$ 5,108