Collaboration Agreements - Summary of Collaboration Revenue (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	$ 5,285	[1]	$ 9,388	$ 36,143	[1]	$ 18,751
Collaborative revenue, excluding revenue from contract with customer	0		5	4		93
Total Collaboration Revenue	5,285		9,393	36,147		18,844
Takeda Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	4,425		9,271	18,597		17,826
Revenue recognized included in the contract liability balance at the beginning of the year				15,600
Sanofi Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total Collaboration Revenue	0		122	15,004		1,018
Sanofi Collaboration Agreement | Peripheral Program License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	0		0	15,000		0
Sanofi Collaboration Agreement | Retained Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	0		117	0		925
Sanofi Collaboration Agreement | Alzheimer's Disease Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, excluding revenue from contract with customer	0		5	4		93
Biogen Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total Collaboration Revenue	860		0	2,546		0
Biogen Collaboration Agreement | Option Research Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenue, revenue from contract with customer	$ 860		$ 0	$ 2,546		$ 0

[1] Includes related party collaboration revenue from a customer of $0.9 million and $2.5 million for the three and nine months ended September 30, 2021, respectively.