Collaboration Agreements - Sanofi (Details) - USD ($)		1 Months Ended	12 Months Ended			86 Months Ended	87 Months Ended
		Nov. 30, 2018	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2025	Dec. 31, 2025
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	[1]		$ 0	$ 0	$ 330,531,000
Performance obligation				0
Collaborative Arrangement | Peripheral Program License | Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer						$ 35,000,000.0
Collaborative Arrangement | CNS Product | Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer						65,000,000.0
Sanofi | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 125,000,000.0
Collaborative revenue, revenue from contract with customer			0	0	$ 25,000,000.0		$ 100,000,000.0
Performance obligation			0			0	0
Sanofi | Collaborative Arrangement | Peripheral Program License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of certain clinical, regulatory and sales milestone events		495,000,000.0
Clinical milestone payment		120,000,000.0
Regulatory milestone payment		175,000,000.0
Commercial milestone payments		$ 200,000,000.0
Sanofi | Collaborative Arrangement | Alzheimer's Disease Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract liability			$ 0	$ 0		$ 0	0
Sanofi | Collaborative Arrangement | Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer							$ 0

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