Leases - Additional Information (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Leases [Abstract]
Operating lease, description		The Company has a non-cancelable facility lease agreement, or the Lease, for office and laboratory facilities in South San Francisco, California, with a remaining lease term of 4.34 years, through January 2024, and a two-year renewal option prior to expiration.
Remaining lease term	4 years 4 months 2 days	4 years 4 months 2 days
Operating lease, renewal term	2 years	2 years
Sublease, description		Company has a non-cancelable sublease agreement for a portion of its facilities through February 2020.
Incremental borrowing rate		9.00%
Cash paid for amounts included in the measurement of the lease liabilities	$ 0.6	$ 1.7