Stockholders' Equity (Narrative) (Details) $ / shares in Units, $ in Millions						1 Months Ended
	Nov. 23, 2021 shares	Dec. 04, 2020 USD ($) $ / shares shares	Jan. 22, 2020 shares	Dec. 24, 2019 USD ($) $ / shares shares	May 07, 2019 USD ($) $ / shares shares	Nov. 30, 2021 USD ($) $ / shares shares	Mar. 31, 2022 vote shares	Dec. 31, 2021 shares	May 03, 2019 closing
Subsidiary, Sale of Stock [Line Items]
Common stock, shares outstanding (in shares)							145,981,180	145,971,184
Common stock voting rights votes | vote							1
Total common shares reserved for future issuance (in shares)							138,203,000
Number of closings | closing									2
Private Placement
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)		24,341,607			9,730,534
Warrants callable (in shares)		18,256,204			9,730,534
Sale of stock price (in usd per share) | $ / shares		$ 0.7464			$ 1.205
Consideration received | $		$ 19.4			$ 16.7
Shares issued upon conversion (in shares)		10			10
Warrants, term					5 years
Warrant exercise price (in usd per share) | $ / shares					$ 1.08
Milestone Closing
Subsidiary, Sale of Stock [Line Items]
Consideration received | $				$ 24.6
2021 Closing
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)						58,923,352
Sale of stock price (in usd per share) | $ / shares						$ 0.36
Consideration received | $						$ 34.6
Shares issued upon conversion (in shares)						10
Preferred Class A | Private Placement
Subsidiary, Sale of Stock [Line Items]
Warrants callable (in shares)					4,158,980
Sale of stock price (in usd per share) | $ / shares					$ 10.80
Nonvoting convertible preferred stock issued (in shares)					415,898
Class A-2 Convertible Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Reverse stock split ratio				10
Class A-2 Convertible Preferred Stock | Milestone Closing
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)				3,288,390
Warrants callable (in shares)				32,883,900
Consideration received | $				$ 26.0
Warrants, term				5 years
Warrant exercise price (in usd per share) | $ / shares				$ 0.666
Class A-3 Convertible Preferred Stock | Private Placement
Subsidiary, Sale of Stock [Line Items]
Warrants callable (in shares)		2,047,276
Sale of stock price (in usd per share) | $ / shares		$ 6.22
Nonvoting convertible preferred stock issued (in shares)		272,970
Warrants, term		5 years
Warrant exercise price (in usd per share) | $ / shares		$ 0.7464
Class A-4 Convertible Preferred Stock | 2021 Closing
Subsidiary, Sale of Stock [Line Items]
Sale of stock price (in usd per share) | $ / shares						$ 3.60
Nonvoting convertible preferred stock issued (in shares)						3,725,720
Warrants | Preferred Class A | Private Placement
Subsidiary, Sale of Stock [Line Items]
Sale of stock price (in usd per share) | $ / shares					$ 0.125
Warrants | Class A-3 Convertible Preferred Stock | Private Placement
Subsidiary, Sale of Stock [Line Items]
Sale of stock price (in usd per share) | $ / shares		$ 0.125
Certain Directors and Executive Officers | Private Placement
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)		833,208			526,083
Certain Directors and Executive Officers | Preferred Class A | Private Placement
Subsidiary, Sale of Stock [Line Items]
Warrants callable (in shares)					526,083
Proceeds from issuance of right to purchase common shares | $					$ 0.6
Certain Directors and Executive Officers | Class A-2 Convertible Preferred Stock | Milestone Closing
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)				121,581
Warrants callable (in shares)				1,215,810
Consideration received | $				$ 1.0
Certain Directors and Executive Officers | Class A-3 Convertible Preferred Stock | Private Placement
Subsidiary, Sale of Stock [Line Items]
Warrants callable (in shares)		624,906
Proceeds from issuance of right to purchase common shares | $		$ 0.6
Directors, Executive Officers and Employees | 2021 Closing
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)						2,222,222
Directors, Executive Officers and Employees | Class A-4 Convertible Preferred Stock | 2021 Closing
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of right to purchase common shares | $						$ 0.8
2019 Plan
Subsidiary, Sale of Stock [Line Items]
Number of additional shares authorized (in shares)			4,166,860
Number of years for increase of authorized shares			10 years
Number of additional shares authorized yearly increase			5.00%
Common stock available for future grant (in shares)							4,452,863
Total common shares reserved for future issuance (in shares)							13,871,693
Inducement Plan
Subsidiary, Sale of Stock [Line Items]
Common stock available for future grant (in shares)							1,800,000
Total common shares reserved for future issuance (in shares)	2,000,000						200,000
Vesting period	4 years
Inducement Plan | Share-based Payment Arrangement, Tranche One
Subsidiary, Sale of Stock [Line Items]
Award vesting percentage	25.00%
Inducement Plan | Share-based Payment Arrangement, Tranche Two
Subsidiary, Sale of Stock [Line Items]
Vesting period for remaining vesting rights	36 months