Regeneron License and Collaboration Arrangement - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2020	Jul. 29, 2016	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licence agreement cumulative revenue recognised						$ 17.9	$ 1.0	$ 8.2
Regeneron Pharmaceuticals, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received	$ 25.0
Additional payment for research funding received	20.0							$ 5.0	$ 5.0
Contract research term period		5 years
Upfront payment		$ 25.0				25.0
Licence agreement additional revenue recognised			$ 5.0
License agreement cumulative revenue reduction recognised				$ 6.6
Increase in estimated transaction price			$ 10.0
Licence agreement cumulative revenue recognised					$ 10.0	31.0	13.1
Contract liability						$ 14.0	$ 21.9
Regeneron Pharmaceuticals, Inc. | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licence agreement additional amount payable of option exercise fees	$ 100.0