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Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Preferred stock shares issued	0		0		0
Revenue—related party	$ 3,028	$ (7,047)	$ 12,493	$ (974)
Regeneron Pharmaceuticals, Inc.
Related Party Transaction [Line Items]
Revenue—related party	3,000	$ (7,000)	12,500	$ (1,000)
Accounts receivable	0		0
Deferred revenue	$ 19,400		$ 19,400
Regeneron Pharmaceuticals, Inc. \| Series B Convertible Preferred Stock [ Member ]
Related Party Transaction [Line Items]
Preferred stock shares issued	883,568		883,568		883,568