PROPERTY AND EQUIPMENT - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment	$ 4,341	$ 4,341
Less: accumulated depreciation and amortization	(4,076)	(3,733)
Property and equipment, net	265	608
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment	3,511	3,511
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	597	597
Office and computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	111	111
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	$ 122	$ 122