Related Parties - Additional Information (Details) - USD ($)		1 Months Ended			3 Months Ended
	Jul. 13, 2020	Feb. 28, 2021	Jan. 31, 2021	May 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	[1]
Related Party Transaction [Line Items]
Cost sharing receivable					$ 5,235,000		$ 1,049,000
Long-term portion of revenue allocated					113,369,000		$ 122,830,000
Research and Development
Related Party Transaction [Line Items]
Reimbursed under cost-sharing provisions of arrangement					(4,924,000)	$ 0
Gilead Collaboration Agreement | Gilead
Related Party Transaction [Line Items]
Revenue recognized					0
Upfront cash payment	$ 175,000,000.0				175,000,000
Unconstrained consideration to be received					100,000,000
Premium on stock purchased	$ 90,600,000
Stock Purchase Agreement | Gilead
Related Party Transaction [Line Items]
Issuance of common stock, shares	5,963,029	5,650,000	5,650,000
Issuance of common stock	$ 200,000,000	$ 220,400,000			220,296,000
Funds received for purchase of common stock					200,000,000
Fair value of stock purchased					109,400,000
Premium on stock purchased					$ 90,600,000
Shares issued, price per share	$ 33.54	$ 39.00	$ 39.00
Gilead
Related Party Transaction [Line Items]
Percentage of outstanding common stock held					19.50%
Number of shares issued				2,200,000
Value of common stock issued				$ 56,700,000
Cost sharing receivable					$ 4,900,000
Deferred revenue					177,700,000
Long-term portion of revenue allocated					110,100,000
Future development and commercialization services contract liability					9,700,000
Gilead | Research and Development
Related Party Transaction [Line Items]
Reimbursed under cost-sharing provisions of arrangement					$ 4,900,000
Gilead | Maximum
Related Party Transaction [Line Items]
Right to purchase additional outstanding voting common stock percentage					35.00%
Gilead | Gilead Collaboration Agreement
Related Party Transaction [Line Items]
Revenue recognized					$ 7,700,000
Reimbursement of milestone expense of cost sharing provisions					4,000,000.0
Gilead | Stock Purchase Agreement
Related Party Transaction [Line Items]
Issuance of common stock, shares	5,963,029	5,650,000
Issuance of common stock		$ 220,400,000			$ 327,800,000
Shares issued, price per share		$ 39.00

[1] The Condensed Consolidated Balance Sheet as of December 31, 2020 has been derived from the audited financial statements as of that date.