License and Acquisition Agreements - Regeneron License Agreement (Details) - Regeneron - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2021
License Agreement
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 5,000
Milestone payment to be paid upon regulatory milestone achievement		$ 7,500			$ 20,000
Research and development expense, Milestone		$ 7,500	$ 0	$ 0
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
Consecutive suspension of activities period for termination of agreement	12 months
Period after which the agreement can be terminated	18 months
Notice period to terminate the agreement	180 days
Notice period to terminate the agreement after US marketing approval of the developed product	1 year
Notice period to terminate the agreement if products are having safety concerns	3 months
Clinical Supply Agreement
License and Acquisition Agreements
Research and development expense related to purchase of drug materials			$ 6,854	$ 1,835
Maximum | License Agreement
License and Acquisition Agreements
Milestone payment to be paid upon regulatory milestone achievement	$ 27,500