Accounting Policies - Common Stock Equivalents Excluded From Computation of Net Loss Per Share (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	18,257	16,082
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	641
Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	25	220
Convertible Debt Securities
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	9,819	9,370