Regeneron License and Collaboration Arrangement - Summary of Change in Company's Contract Liabilities (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2020	Sep. 30, 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]	(12,493)	974
Balance at end of period		$ 19,390	$ 23,852

[1] Additions (deductions) to contract liabilities relate to deferred revenue derecognized (recognized) as revenue during the reporting period.