PROPERTY AND EQUIPMENT, NET - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 13,223	$ 13,223
Less: Accumulated depreciation and amortization	(11,308)	(10,786)
Property and equipment, net	1,915	2,437
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,680	2,680
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	20	20
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 10,523	$ 10,523