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Collaboration, License and Success Payment Agreements - Additional Information (Details) - USD ($) | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Jun. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020 | Jun. 30, 2021 | Apr. 30, 2021 | Jul. 31, 2019 | May 31, 2019
Fred Hutch Collaboration Agreement [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Collaboration agreement expense | $ 1,100,000 | $ 1,000,000.0 |  | $ 3,100,000 | $ 3,000,000.0 |  |  |  |  |
Fair value of success payments net | 21,700,000 |  |  | 21,700,000 |  | $ 8,000,000.0 |  |  |  |
Success payment expense | $ (800,000) | 1,200,000 |  | $ 14,100,000 | 3,800,000 |  |  |  |  |
Estimated fair value per share | $ 1.83 |  |  | $ 1.83 |  |  |  |  |  |
Fred Hutch Collaboration Agreement [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate success payment |  |  |  | $ 10,000,000.0 |  |  |  |  |  |
Share issued price per share | 18.29 |  |  | $ 18.29 |  |  |  |  |  |
Fred Hutch Collaboration Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate success payment |  |  |  | $ 200,000,000.0 |  |  |  |  |  |
Share issued price per share | $ 91.44 |  |  | $ 91.44 |  |  |  |  |  |
Fred Hutch Collaboration Agreement [Member] | Maximum [Member] | 50x [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate success payment |  |  |  | $ 200,000,000.0 |  |  |  |  |  |
Stanford Collaboration Agreement [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Collaboration agreement expense | $ 800,000 | 0 |  | 2,300,000 | 0 |  |  |  |  |
Fair value of success payments net | 23,100,000 |  |  | 23,100,000 |  | 8,900,000 |  |  |  |
Success payment expense | $ 1,000,000.0 | 0 |  | $ 5,200,000 | 0 |  |  |  |  |
Estimated fair value per share | $ 1.83 |  |  | $ 1.83 |  |  |  |  |  |
Stanford Collaboration Agreement [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate success payment |  |  |  | $ 10,000,000.0 |  |  |  |  |  |
Share issued price per share | 18.29 |  |  | $ 18.29 |  |  |  |  |  |
Stanford Collaboration Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate success payment |  |  |  | $ 200,000,000.0 |  |  |  |  |  |
Share issued price per share | $ 91.44 |  |  | $ 91.44 |  |  |  |  |  |
Stanford Collaboration Agreement [Member] | Maximum [Member] | 50x [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate success payment |  |  |  | $ 200,000,000.0 |  |  |  |  |  |
GSK Agreement [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Agreement upfront consideration | $ 45,000,000.0 |  |  | 45,000,000.0 |  |  |  |  | $ 45,000,000.0 |
Maximum potential future development and sales milestone payment |  |  |  |  |  |  |  | $ 400,000,000.0 |  |
Maximum potential future technology validation milestone payment | 200,000,000.0 |  |  | 200,000,000.0 |  |  |  |  |  |
Transaction price, revenue contract |  |  |  | 103,600,000 |  |  |  |  |  |
Revenue recognized | 2,600,000 | $ 1,100,000 |  | 7,700,000 | $ 5,400,000 |  |  |  |  |
Additional allocated upfront consideration |  |  |  | 58,600,000 |  |  |  |  |  |
GSK License Contract [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Contract assets | 0 |  |  | 0 |  |  |  |  |  |
Contract liabilities | 0 |  |  | 0 |  |  |  |  |  |
Revenue recognized | 0 |  |  | 0 |  |  |  |  |  |
PACT Agreement [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Total upfront payment for collaboration agreement |  |  | $ 63,600,000 |  |  |  |  |  |  |
License fees |  |  | $ 50,000,000.0 |  |  |  |  |  |  |
Shares purchased |  |  | 17,806,901 |  |  |  |  |  |  |
Share price |  |  | $ 2.81 |  |  |  |  |  |  |
Estimated shares purchased, fair value per share |  |  | $ 2.05 |  |  |  |  |  |  |
Additional allocated upfront purchase price |  |  | $ 13,600,000 |  |  |  |  |  |  |
PACT Agreement [Member] | Other Investment [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Strategic equity investment |  |  | $ 36,400,000 |  |  |  |  |  |  |
G S K Already in Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum potential future development and sales milestone payment | 400,000,000.0 |  |  | 400,000,000.0 |  |  |  |  |  |
G S K Not Already in Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum potential future development and sales milestone payment | $ 900,000,000.0 |  |  | $ 900,000,000.0 |  |  |  |  |  |
NCI License Agreement [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Agreement upfront consideration |  |  |  |  |  | 100,000 | $ 25,000 |  |  |
Maintenance cost |  |  |  |  |  | 3,100 |  |  |  |
Total consideration |  |  |  |  |  | 103,100 |  |  |  |
Prespecified development milestone payment |  |  |  |  |  | 3,100,000 | $ 75,000 |  |  |
Pre-specified commercial milestone payment |  |  |  |  |  | $ 12,000,000.0 |  |  |  |
Series AA Convertible Preferred Stock | GSK Agreement [Member] |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |
Share price |  |  |  |  |  |  |  |  |  | $ 6.78
Total upfront consideration |  |  |  |  |  |  |  |  |  | $ 103,600,000
Shares, issued |  |  |  |  |  |  |  |  |  | 30,253,189
Estimated fair value per share | $ 4.84 |  |  | $ 4.84 |  |  |  |  |  |
Share price | $ 6.78 |  |  | $ 6.78 |  |  |  |  |  |
Additional allocated upfront consideration |  |  |  | $ 58,600,000 |  |  |  |  |  |

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