Stockholders' Equity (Deficit)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Stockholders' Equity (Deficit)	Stockholders' EquityDuring the nine months ended September 30, 2021 and 2020, the Company sold 2.6 million and 29.1 million, respectively, of shares of its common stock resulting in net proceeds of approximately $565 million and $446 million, respectively, under its various At Market Issuance Sales agreements. In June 2021, the Company entered into an At Market Issuance Sales Agreement (the "June 2021 Sales Agreement"), which allows it to issue and sell up to $500 million in gross proceeds of shares of its common stock, and terminated its existing At Market Issuance Sales agreement. As of September 30, 2021, no shares had been sold under the June 2021 Sales Agreement