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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 |  |  |

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