Balance Sheet Details (Property and Equipment) (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 11,451,000	$ 11,102,000
Less: accumulated depreciation	(9,336,000)	(9,055,000)
Property and equipment, net	2,115,000	2,047,000
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	6,870,000	6,547,000
Office and Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	418,000	413,000
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	740,000	719,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,423,000	$ 3,423,000