Collaboration, License and Success Payment Agreements - Narrative (Details)	1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($) $ / shares shares	May 31, 2019 $ / shares shares	Dec. 31, 2021 USD ($) performance_obligation	Jun. 30, 2020 USD ($) $ / shares	Dec. 31, 2021 USD ($) performance_obligation	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) collaboration_target payment representative	Apr. 30, 2021 USD ($)	Oct. 31, 2020 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense							$ 138,693,000	$ 182,243,000	$ 63,595,000
Impairment of other investments							36,447,000	0	0
PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments					$ 36,400,000
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
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							4,200,000	4,100,000	3,700,000
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		$ 8,000,000			8,500,000		8,500,000	8,000,000
Success payment liability		5,200,000			6,400,000		6,400,000	5,200,000
Success payment expenses							1,200,000	4,800,000	400,000
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	800,000
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		8,900,000			9,900,000		9,900,000	8,900,000
Success payment liability		600,000			3,100,000		3,100,000	600,000
Success payment expenses							2,500,000	600,000
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]
Contract liabilities		95,161,000			84,653,000		84,653,000	95,161,000
Revenue							10,500,000	7,800,000	$ 700,000
Revenue recognized during the period previously recorded in deferred revenue							10,508,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | GSK | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of initial collaboration targets | collaboration_target									2
Number of additional collaboration targets | collaboration_target									7
Number of representatives of JSC appointed by company | representative									3
Contract liabilities		45,000,000			$ 0		$ 0	45,000,000	$ 45,000,000
Revenue, Remaining Performance Obligation, Variable Consideration Amount, Number Of One-Time Payments | payment									2
Stock Purchase Agreement portion of transaction price		58,600,000						58,600,000
Transaction price		103,600,000						103,600,000
Number of performance obligations | performance_obligation					2		2
Revenue							$ 0
Contract assets					$ 0		0
Capitalized contract costs					$ 0		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 | GSK | Maximum | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone payments, within pipeline									$ 400,000,000
Potential milestone payments, not within pipeline									900,000,000
Potential milestone payments, technology validation									$ 200,000,000
Variable consideration amount										$ 400,000,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment			$ 50,000,000
Stock purchase agreement, stock purchased (in shares) | shares			17,806,901
Stock purchase agreement, purchase price per share (in dollars per share) | $ / shares			$ 2.81
Stock purchase agreement, fair value per share (in dollars per share) | $ / shares						$ 2.05
Additional purchase price consideration			$ 13,600,000			$ 13,600,000
Total upfront payment paid			63,600,000			63,600,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PACT | Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Strategic equity investment			$ 36,400,000			$ 36,400,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | NCI
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense		100,000
Upfront payment	$ 25,000
Maintenance fees							$ 75,000	3,100
Maximum aggregate development milestone payments	$ 75,000	3,100,000						3,100,000
Maximum aggregate commercial milestone payments		$ 12,000,000						$ 12,000,000