Operating Leases - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Operating Leased Assets [Line Items]
Right-of-use assets	$ 5,515		$ 5,515		$ 5,057
Operating lease liability	7,086		7,086
Operating lease cost	$ 400	$ 400	1,100	$ 1,200
Cash paid included in operating lease liabilities included in cash flow from operating activities			$ 1,200
South San Francisco, California
Operating Leased Assets [Line Items]
Operating lease, remaining lease term	3 years 9 months 18 days		3 years 9 months 18 days
Operating lease, discount rate	7.00%		7.00%
South San Francisco, California | Second Amendment
Operating Leased Assets [Line Items]
Operating lease, discount rate	6.00%		6.00%
South San Francisco, California | Lease Agreement | Laboratory and Office Facilities
Operating Leased Assets [Line Items]
Lease expiration date			Jul. 31, 2024
South San Francisco | Laboratory and Office Facilities | Second Amendment
Operating Leased Assets [Line Items]
Right-of-use assets	$ 1,200		$ 1,200
Operating lease liability	$ 1,200		$ 1,200
Operating lease commencement month and year			2020-08