Summary of Significant Accounting Policies - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands							3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 13, 2021	Feb. 16, 2021	Feb. 11, 2021	Nov. 25, 2020	Jun. 19, 2020	Mar. 03, 2020	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Working capital deficiency									$ 78,800
Cash and cash equivalents									52,480	$ 17,996
Short-term investments									43,125	7,998
Net loss attributable to common stockholders, diluted							$ (36,602)	$ (34,400)	(77,316)	(29,229)
Net loss attributable to common stockholders, basic							$ (36,602)	$ (34,400)	(77,316)	(29,229)
Number of shares sold under offering (in shares)		15,800,000	3,000,000
Warrants granted (in shares)		44,305,088
Net proceeds from issuance of common stock and warrants		$ 77,900							77,852	55,352
Net proceeds from issuance of preferred stock and warrants	$ 50,600								$ 50,585	$ 0
Aggregate offering amount					$ 150,000
Registered Direct Offering
Class of Stock [Line Items]
Subscription price (in usd per share)	$ 920
Original issuance discount percentage	8.00%
Aggregate subscription value	$ 54,100
Series 7 Preferred Stock | Registered Direct Offering
Class of Stock [Line Items]
Number of shares sold under offering (in shares)	58,750
Purchase Agreement
Class of Stock [Line Items]
Number of shares sold under offering (in shares)				5,000,000
Warrants granted (in shares)		28,505,088		8,000,000
Warrant exercise price (in usd per share)		$ 0.001		$ 1.25
Purchase price per unit (in usd per share)				$ 1.25
Warrant | Registered Direct Offering
Class of Stock [Line Items]
Number of shares sold under offering (in shares)	47,000,000
Maxim Warrant
Class of Stock [Line Items]
Aggregate offering amount					$ 150,000	$ 50,000
ATM
Class of Stock [Line Items]
Number of shares sold under offering (in shares)										33,416,830
NetProceedsFromPublicOffering										$ 46,100
2020 Pre-Funded Warrant
Class of Stock [Line Items]
Warrants granted (in shares)				3,000,000
Warrant exercise price (in usd per share)				$ 0.001
Purchase price per unit (in usd per share)				$ 1.249
NetProceedsFromPublicOffering				$ 9,200
Maximum
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		1.55
Purchase price per unit (in usd per share)		2.01
Minimum
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		2.01
Purchase price per unit (in usd per share)		$ 1.549