In-license, Acquisition and Collaboration Agreements - Biogen Asset Purchase Agreement (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
License and Acquisition Agreements
Uncured period which causes termination of the agreement, due to insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured	90 days
Notice period to terminate the agreement under payment-related breaches	30 days
Research and development			$ 13,798	$ 23,945	$ 34,615	$ 52,628
Asset Purchase Agreement | Biogen
License and Acquisition Agreements
Remaining milestone payments to be paid upon clinical and regulatory milestone achievement			$ 165,000		165,000
Maximum aggregate obligation to pay insignificant annual maintenance fees as well as clinical and regulatory milestone payments		$ 1,575
Notice period to terminate the agreement		90 days
Uncured period which causes termination of the agreement, due to insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured		90 days
Notice period to terminate the agreement under payment-related breaches		30 days
Research and development				$ 14	$ 34	$ 28
Asset Purchase Agreement | Biogen | Maximum
License and Acquisition Agreements
Milestone payment to be paid upon clinical and regulatory milestone achievement		$ 179,000
Milestone payment to be paid upon net sales milestone achievement		$ 150,000