Property and Equipment - Net Property and Equipment at Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Total property and equipment, at cost	$ 877	$ 871
Less: Accumulated depreciation and amortization	833	774
Property and equipment, net	44	97
Leasehold improvements
Property, Plant and Equipment
Total property and equipment, at cost	107	107
Laboratory equipment and other
Property, Plant and Equipment
Total property and equipment, at cost	$ 770	$ 764