Significant Agreements - Novartis Agreements (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Mar. 04, 2022 USD ($) item	Jan. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) item	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 28, 2023 USD ($) shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Purchase of common stock			$ 31,121
Collaboration revenue			250,008	$ 40,907	$ 37,415
Related party collaboration receivable			3,341	$ 257
Novartis Pharma, AG | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment			80,000
Shares of common stock | shares						2,145,002
Aggregate purchase price						$ 20,000
Allocation of fixed consideration			$ 80,000
Number of days written notice required by reporting entity to terminate agreement			90 days
Costs to obtain collaboration agreement			$ 1,900
Revenue recognized			80,000
Related party collaboration receivable			80,000
Contract expense			1,900
Novartis Pharma, AG | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of transgenes | item	3
Number of additional targets | item	2
Upfront payment	$ 54,000
Number of license options | item	3
Number of license options on additional targets | item	5
Number of license option exercise for each target | item	1
Number of alliance managers | item	2
Number of options | item	1
Number of major market countries received regulatory approval | item	3
Number of days written notice required by reporting entity to terminate agreement	90 days
Number of performance obligations | item	3
Number of material rights | item	3
Allocation of transaction price	$ 18,000		25,000
Revenue recognized			79,000
Collaboration revenue			79,000
Novartis Pharma, AG | Option and license agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of license options | item	1
Novartis Pharma, AG | First and Second Material Right
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of transaction price			54,000
Novartis Pharma, AG | Subsequent events | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount of premium		$ 700
Novartis Pharma, AG | Sales milestone | 2023 Novartis Collaboration Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of variable consideration			775,000
Novartis Pharma, AG | Development milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of variable consideration			425,000
Novartis Pharma, AG | SMA Program | Development, regulatory and commercialization milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			200,000
Novartis Pharma, AG | SMA Program | Sales milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			400,000
Novartis Pharma, AG | HD Program | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of variable consideration			24,200
Novartis Pharma, AG | HD Program | Development, regulatory and commercialization milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			225,000
Novartis Pharma, AG | HD Program | Sales milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			$ 375,000
Novartis Pharma, AG | Discovery Programs 2023 | 2023 Novartis Collaboration Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of options | item			4