Collaboration Agreements - Biogen (Details)		1 Months Ended	3 Months Ended		44 Months Ended	66 Months Ended
		Aug. 31, 2023 program	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	[1]		$ 107,016,000	$ 128,816,000
Collaboration revenue from customers	[2]		0	35,141,000
Biogen | Biogen Amendment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of TV-enabled programs in which rights of first negotiation were waived | program		2
Biogen | Biogen Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development			4,800,000	4,200,000
Cost sharing payments due			4,800,000	$ 3,200,000	$ 4,800,000	$ 4,800,000
Biogen | Biogen Collaborative Arrangement | Option Fee Payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue from customers					5,000,000
Biogen | Biogen Collaborative Arrangement | Milestone Triggered
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue from customers					0
Biogen | Biogen Collaborative Arrangement | Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue from customers					0
Sanofi | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract liability			$ 0		$ 0	0	$ 0
Sanofi | Collaborative Arrangement | Milestone Triggered
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue from customers						100,000,000
Sanofi | Collaborative Arrangement | Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue from customers						$ 0

[1] Includes expenses for cost sharing payments due to a related party of $4.2 million for the three months ended March 31, 2023.

[2] Includes related-party collaboration revenue from customers of $0.1 million for the three months ended March 31, 2023.