Commitments and Contingencies - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) ft²	Sep. 30, 2019 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Commitments And Contingencies [Line Items]
Operating leases, number of square feet | ft²	83,000
Operating leases remaining lease terms	111 months
Operating lease right-of-use assets	$ 25,070
Initial lease liability	29,814
Accumulated deficit	245,736			$ 152,221
Operating lease expense	4,400	$ 1,700
Operating lease, payments	$ 3,600
Operating lease, weighted-average remaining lease term	8 years 10 months 24 days
Operating lease, weighted -average discount rate	8.90%
Property and Equipment
Commitments And Contingencies [Line Items]
Construction in progress				$ 2,100
Tenant improvements recorded as leasehold improvements and furniture and fixtures	$ 13,300
ASC 842
Commitments And Contingencies [Line Items]
Initial lease receivables			$ 2,700
Operating lease right-of-use assets			22,300
Deferred rent balance			2,300
Initial lease liability			27,300
Operating lease, option to extend	true
Operating lease, option to extend, description	The option to extend its leases in San Diego was not recognized as part of the lease liability and ROU lease assets.
ASC 842 | Cumulative Adjustment
Commitments And Contingencies [Line Items]
Accumulated deficit			100
ASC 842 | Adoption of ASC 842 Adjustment | Property and Equipment
Commitments And Contingencies [Line Items]
Derecognition of construction in progress related to manufacturing facility			2,100
ASC 842 | Adoption of ASC 842 Adjustment | Other Long-Term Liabilities
Commitments And Contingencies [Line Items]
Derecognition of construction financing obligation related to manufacturing facility			2,500
ASC 842 | Adoption of ASC 842 Adjustment | Prepaid and Other Current Assets
Commitments And Contingencies [Line Items]
Derecognition of other receivables related to manufacturing facility			$ 300
Maximum
Commitments And Contingencies [Line Items]
Operating lease remaining lease term dedicated to manufacturing suites	6 months