Balance Sheet Details (Property and Equipment) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 10,459,000	$ 10,345,000
Less: accumulated depreciation	(8,454,000)	(8,158,000)
Property and equipment, net	2,005,000	2,187,000
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	6,127,000	6,047,000
Office and Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	334,000	323,000
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	646,000	646,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,352,000	$ 3,329,000