Collaboration Agreements - Sanofi (Details) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		24 Months Ended
	Jul. 31, 2019 USD ($)	Nov. 30, 2018 USD ($) indication	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of indications | indication		3
Sales			$ 9,388	$ 13,508	$ 18,751	$ 21,717
Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Funded percentage		30.00%
Sanofi | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Funded percentage		70.00%
Sanofi | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 125,000
Milestone payments upon achievement of certain clinical, regulatory and sales milestone events		1,100,000
Increase in transaction price							$ 21,300
Receivable			100		100		100	$ 1,200
Sanofi | Collaborative Arrangement | CNS Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Clinical milestone payment		215,000
Regulatory milestone payment		385,000
Sanofi | Collaborative Arrangement | Peripheral Program License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Clinical milestone payment		120,000
Regulatory milestone payment		175,000
Commercial milestone payments		$ 200,000
Sanofi | Collaborative Arrangement | Retained Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in transaction price			$ 100	2,400	$ 900	9,200	11,300
Sanofi | Collaborative Arrangement | Milestone Triggered
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales	$ 10,000						10,000
Sanofi | Collaborative Arrangement | Milestone Triggered and Retained Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in transaction price				$ 12,400		$ 19,200
Sanofi | Collaborative Arrangement | Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales							$ 0