Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2020 USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Number of reportable segments | Segment	1
Impairment charges	$ 0	$ 0	$ 0
Trailer bill	0
Right-of-use assets	12,781,000
Operating lease, liabilities	18,110,000
Operating lease, current liabilities	2,867,000
Operating lease liabilities, noncurrent	15,243,000
Deferred rent balance		3,734,000
Accumulated deficit	$ (328,184,000)	$ (205,326,000)
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Change in Accounting Principle, Accounting Standards Update, Early Adoption [true false]	true
ASU 2018-18
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-15
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Right-of-use assets				$ 5,800,000
Operating lease, liabilities				10,100,000
Operating lease, current liabilities				1,200,000
Operating lease liabilities, noncurrent				8,900,000
Deferred rent balance				4,300,000
ASU 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Accumulated deficit				$ 0
ASU 2016-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Brisbane, California
Significant Accounting Policies [Line Items]
Operating lease expiration year	2031
Operating lease commencement year	2021
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	1 year
Operating lease expiration year	2025
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	5 years
Operating lease expiration year	2029