Stockholders' Deficit - Common Stock and Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended				12 Months Ended
	Feb. 08, 2021	Mar. 31, 2021	Feb. 28, 2021	Nov. 30, 2020	Oct. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Shares issued for exercise of options (in shares)						111,000	1,182,000	344,000
Number of shares under warrants granted							4,752,116
Outside Consultant [Member]
Class Of Stock [Line Items]
Number of shares under warrants granted								75,000
Warrant [Member]
Class Of Stock [Line Items]
Weighted average grant date fair value							$ 1.56	$ 3.00
Expected term							10 years	5 years
Volatility rate							68.80%	60.80%
Dividend yields							0.00%	0.00%
Risk-free interest rate							0.30%	2.50%
Common Stock [Member]
Class Of Stock [Line Items]
Proceeds from stock plans			$ 96.6	$ 31.7	$ 77.0
Shares issued for sale of common stock, net of cost (in shares)			59,459,460	26,953,125	29,900,000	121,765,000	26,953,000	29,900,000
Shares Issued, Price Per Share			$ 1.85	$ 1.28	$ 2.75
Shares issued for exercise of options (in shares)				3,515,625	3,900,000	111,000	1,182,000	344,000
2021 ATM Program [Member] | Common Stock [Member]
Class Of Stock [Line Items]
Public offering of common stock authorized for sale		$ 100.0
Percentage of commission rate gross sales price		3.00%
Sale of stock, number of shares issued in transaction						33,705,315
Sale of stock, price Per share						$ 1.21
Proceeds from stock plans						$ 39.4
2020 ATM Program [Member] | Common Stock [Member]
Class Of Stock [Line Items]
Public offering of common stock authorized for sale				$ 50.0
Percentage of commission rate gross sales price				3.00%
Sale of stock, number of shares issued in transaction	28,600,689
Sale of stock, price Per share	$ 1.75
Proceeds from stock plans	$ 48.1