LEASES - NARRATIVE (Details) $ in Thousands		3 Months Ended
	Mar. 12, 2020 USD ($)	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020	Jun. 30, 2020 USD ($)	Jan. 31, 2020 ft²	Nov. 12, 2014 ft²
Leases
Operating lease liabilities		$ 2,008		$ 3,059
Right-of-use assets		1,075		$ 1,607
Operating Lease, Initial Direct Cost Expense, over Term	$ 300
Operating Lease, Weighted Average Discount Rate, Percent					3.50%
Prepaid Expenses and Other Current Assets [Member]
Leases
Operating Lease, Initial Direct Cost Expense, over Term		100
Other Assets [Member]
Leases
Operating Lease, Initial Direct Cost Expense, over Term		100
San Francisco California Facility
Leases
Area | ft²							5,000
Operating lease liabilities						$ 600
Right-of-use assets						$ 600
Operating Lease, Weighted Average Discount Rate, Percent							3.50%
Operating Lease, Impairment Loss		$ 32	$ 300
San Jose California Facility
Leases
Area | ft²								42,000