Collaboration Agreements - Schedule of Collaboration Revenue (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue		$ 0	$ 0	$ 330,531
Collaborative revenue, revenue from contract with customer	[1]	0	0	330,531
Related Party
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer				295,500
Takeda Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue		0	0	10,000
Sanofi Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue		0	0	25,000
Biogen Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue		0	0	295,531
Biogen Collaboration Agreement | ATV:Abeta Program License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer		0	0	293,912
Biogen Collaboration Agreement | ATV:Abeta Program License | Related Party
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer				288,900
Biogen Collaboration Agreement | Option Research Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer		$ 0	$ 0	$ 1,619

[1] Includes related-party collaboration revenue from customers of $295.5 million for the year ended December 31, 2023.