Regeneron License and Collaboration Arrangement - Summary of Change in Company's Contract Liabilities (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Contract Asset
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additions		$ 10,000
Additions (Deductions)	[1]	(10,000)
Contract Liability
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of period		21,883	$ 22,878
Additions		10,000
Additions (Deductions)	[1]	(17,903)	(995)
Balance at end of period		$ 13,980	$ 21,883

[1] Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.