Description of Business (Details) - USD ($)	1 Months Ended
	Jun. 30, 2020	Jan. 31, 2020	Sep. 30, 2020	Dec. 31, 2019		Nov. 30, 2019
Subsidiary, Sale of Stock [Line Items]
Stock issuance, maximum value						$ 250,000,000.0
Stock issuance, maximum compensation due to third party (as a percent)				3.00%
Issuance of common stock (in shares)		570,839
Stock issues during period, value	$ 595,700,000	$ 14,800,000
Shares sold in transaction (in shares)	13,457,447
Offering price (in dollars per share)	$ 47.00
Gross proceeds from sale of stock	$ 632,500,000
Cash and cash equivalents and marketable securities			$ 1,000,000,000.0
Accumulated deficit			$ 577,773,000	$ 396,122,000	[1]
Underwriters' Option
Subsidiary, Sale of Stock [Line Items]
Shares sold in transaction (in shares)	1,755,319

[1] The balance sheet as of December 31, 2019 is derived from the audited financial statements as of that date.