Regeneron License and Collaboration Arrangement - Summary of Change in Company's Contract Liabilities (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020
Contract Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of period			$ 0
Additions			10,000
Additions (Deductions) (1)	[1]		(10,000)
Balance at end of period			0
Contract Liability
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of period		$ 13,980	21,883
Additions		370	10,000
Additions (Deductions) (1)	[1]	(4,262)	(12,493)
Balance at end of period		$ 10,088	$ 19,390

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