License, Collaboration and Success Payment Agreements - Narrative (Details)		1 Months Ended		12 Months Ended
	Oct. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)	May 31, 2019 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($) $ / shares	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				$ 182,945,000	$ 159,188,000	$ 138,693,000
Reduction in net loss				$ (234,632,000)	$ (183,118,000)	$ (250,219,000)
Reduction in net loss per common share, basic (in dollars per share) | $ / shares				$ (0.93)	$ (0.74)	$ (1.84)
Reduction in net loss per common share, diluted (in dollars per share) | $ / shares				$ (0.93)	$ (0.74)	$ (1.84)
Impairment of other investments				$ 12,923,000	$ 5,000,000	$ 36,447,000
Gain on other investments				0	2,923,000	0
PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments		$ 36,400,000				36,400,000
Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments				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
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
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Fred Hutch
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				900,000	1,700,000	4,200,000
Potential aggregate success payments				0
Term of success payment agreement										9 years
Trigger period from IPO date										1 year
Trigger period thereafter										2 years
Success payment expense/(gain)				(1,900,000)	(3,900,000)	1,200,000
Fair value of potential success payments due				700,000	2,500,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Fred Hutch | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance										10
Potential aggregate success payments										$ 10,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares										$ 18.29
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Fred Hutch | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance										50
Potential aggregate success payments										$ 200,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares										$ 91.44
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Stanford
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				3,000,000	3,000,000	3,000,000
Potential aggregate success payments				0
Term of success payment agreement							9 years
Trigger period from IPO date							1 year
Trigger period thereafter							2 years
Success payment liability				900,000	1,900,000
Success payment expense/(gain)				(900,000)	(1,200,000)	2,500,000
Fair value of potential success payments due				1,100,000	3,300,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Stanford | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Commercial milestone payments due									2,500,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Stanford | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance							10
Potential aggregate success payments							$ 10,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares							$ 18.29
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Stanford | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance							50
Potential aggregate success payments							$ 200,000,000
Per share common stock price required for payment (in dollars per share) | $ / shares							$ 91.44
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | Stanford | Maximum | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone payments due									$ 3,700,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | GSK
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue				0	84,700,000	$ 10,500,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | GSK | Adjustment To Revenue Related To Change In Estimate
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue					83,600,000
Reduction in net loss					$ 83,600,000
Reduction in net loss per common share, basic (in dollars per share) | $ / shares					$ 0.34
Reduction in net loss per common share, diluted (in dollars per share) | $ / shares					$ 0.34
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | GSK | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract liabilities			$ 45,000,000	0
Stock Purchase Agreement portion of transaction price			58,600,000
Transaction price			$ 103,600,000
Contract assets				$ 0
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | GSK | Series AA Convertible Preferred Stock | License
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
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Strategic equity investment								$ 36,400,000