LEASES - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)	Jan. 31, 2020 ft²	Nov. 12, 2014 ft²
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 3,059	$ 3,814	$ 3,059	$ 3,814
Operating lease, borrowing rate	3.50%	3.25%	3.50%	3.25%
Right-of-use assets	$ 1,607	$ 2,202	$ 1,607	$ 2,202
Sublease, initial direct costs			300
Impairment of right-of-use lease asset			271	$ 939
Prepaid Expenses and Other Current Assets
Lessee, Lease, Description [Line Items]
Sublease, initial direct costs			100
Other Assets
Lessee, Lease, Description [Line Items]
Sublease, initial direct costs			$ 100
San Francisco California Facility
Lessee, Lease, Description [Line Items]
Operating lease liabilities					$ 600
Operating lease, borrowing rate					3.50%
Right-of-use assets					$ 600
Area | ft²						5,000
Impairment of right-of-use lease asset	$ 300
San Jose California Facility
Lessee, Lease, Description [Line Items]
Area | ft²							42,000
Impairment of right-of-use lease asset		$ 900