License, Collaboration, and Success Payment Agreements - Narrative (Details)		1 Months Ended	3 Months Ended			9 Months Ended
	Oct. 01, 2022 USD ($)	May 31, 2019 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($)	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2022 USD ($) $ / shares	Dec. 31, 2022 USD ($)	Oct. 31, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) $ / shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense			$ 43,849,000	$ 41,607,000		$ 135,950,000	$ 121,156,000
Net loss			$ (50,853,000)	$ (70,254,000)		$ (181,702,000)	$ (174,721,000)
Net loss per common share, basic (in dollars per share) | $ / shares			$ (0.20)	$ (0.28)		$ (0.73)	$ (0.71)
Net loss per common share, diluted (in dollars per share) | $ / shares			$ (0.20)	$ (0.28)		$ (0.73)	$ (0.71)
Impairment of other investments			$ 0	$ 5,000,000		$ 12,923,000	$ 5,000,000
PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments					$ 36,400,000
Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments				5,000,000		10,000,000	5,000,000
Series A Convertible Preferred Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Convertible preferred stock, par value (in dollars per share) | $ / shares									$ 1.83			$ 1.83
Fred Hutch | GSK Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual license maintenance payments												$ 50,000
Aggregate research payments due												$ 12,000,000
Term of collaborative arrangement for research												6 years
Research and development expense			300,000	400,000		700,000	1,400,000
Aggregate success payment(s) (in millions)			0			0
Term of success payment agreement												9 years
Trigger period from IPO date												1 year
Trigger period thereafter												2 years
Fair value of potential success payments due			400,000			400,000		$ 2,500,000
Success payment expense (gain)			(1,500,000)	1,400,000		(2,100,000)	800,000
Fred Hutch | GSK Agreement | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance												10
Aggregate success payment(s) (in millions)												$ 10,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares												$ 18.29
Fred Hutch | GSK Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance												50
Aggregate success payment(s) (in millions)												$ 200,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares												$ 91.44
Stanford | GSK Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual license maintenance payments											$ 50,000
Aggregate research payments due									$ 12,000,000
Term of collaborative arrangement for research									4 years
Research and development expense			800,000	800,000		2,300,000	2,300,000
Aggregate success payment(s) (in millions)			0			0
Term of success payment agreement									9 years
Trigger period from IPO date									1 year
Trigger period thereafter									2 years
Fair value of potential success payments due			800,000			800,000		3,300,000
Success payment expense (gain)			(1,200,000)	1,000,000		(1,200,000)	1,400,000
Success payment liability			600,000			600,000		1,900,000
Stanford | GSK Agreement | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone payments due											2,500,000
Stanford | GSK Agreement | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance									10
Aggregate success payment(s) (in millions)									$ 10,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares									$ 18.29
Stanford | GSK Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance									50
Aggregate success payment(s) (in millions)									$ 200,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares									$ 91.44
Stanford | GSK Agreement | Maximum | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone payments due											$ 3,700,000
GSK | GSK Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized			0	$ 0		0	36,300,000
GSK | GSK Agreement | Change in Collaboration and License Agreement estimate
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized							35,300,000
Net loss							$ 35,300,000
Net loss per common share, basic (in dollars per share) | $ / shares							$ 0.14
Net loss per common share, diluted (in dollars per share) | $ / shares							$ 0.14
GSK | GSK Agreement | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract liabilities		$ 45,000,000	0			0		0
Stock purchase agreement portion of transaction price		58,600,000
Transaction price		$ 103,600,000
Contract assets			$ 0			0		$ 0
GSK | GSK Agreement | License | Series AA Convertible Preferred Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Stock sold under stock purchase program (in shares) | shares		30,253,189
Price per share of stock sold under stock purchase program (in dollars per share) | $ / shares		$ 6.78
Fair value per share of stock sold under stock purchase program (in dollars per share) | $ / shares		$ 4.84
PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Gain on other investments	$ 2,900,000
PACT | Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments						$ 2,900,000
PACT | GSK Agreement | Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Strategic equity investment										$ 36,400,000