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Nonvoting Convertible Preferred Stock Issued

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Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Yearly Increase

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Exercise price per share or per unit of warrants or rights outstanding.

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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Aggregate number of common shares reserved for future issuance.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Number of shares issued for each share of convertible preferred stock that is converted.

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Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholder, which takes precedence over common stockholders in the event of liquidation and from issuance of rights to purchase common shares at a predetermined price.

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Cash received on stock transaction after deduction of issuance costs.

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The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

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Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

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Number of additional shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Stockholders' Equity (Narrative) (Details) $ / shares in Units, $ in Millions	Dec. 04, 2020 USD ($) $ / shares shares	Jan. 22, 2020 shares	Dec. 24, 2019 USD ($) $ / shares shares	May 07, 2019 USD ($) $ / shares shares	May 03, 2019 USD ($) shares	Oct. 02, 2018	Mar. 31, 2021 vote shares	Dec. 31, 2020 shares
Subsidiary, Sale of Stock [Line Items]
Common stock, shares outstanding (in shares)							74,689,132	67,432,712
Common stock voting rights votes \| vote							1
Total common shares reserved for future issuance (in shares)							91,967,000
Reverse stock split ratio						0.0833
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 (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 (usd per share) \| $ / shares				$ 1.08
Milestone Closing
Subsidiary, Sale of Stock [Line Items]
Consideration received \| $			$ 24.6
Preferred Class A \| Private Placement
Subsidiary, Sale of Stock [Line Items]
Warrants callable (in shares)				4,158,980
Sale of stock price (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 (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 (usd per share) \| $ / shares	$ 6.22
Nonvoting convertible preferred stock issued (in shares)	272,970
Warrants, term	5 years
Warrant exercise price (usd per share) \| $ / shares	$ 0.622
Warrant \| Preferred Class A \| Private Placement
Subsidiary, Sale of Stock [Line Items]
Sale of stock price (usd per share) \| $ / shares				$ 0.125
Warrant \| Class A-3 Convertible Preferred Stock \| Private Placement
Subsidiary, Sale of Stock [Line Items]
Sale of stock price (usd per share) \| $ / shares	$ 0.125
Directors, Executive Officers and Employees \| Private Placement
Subsidiary, Sale of Stock [Line Items]
Share sold (in shares)	833,208				526,083
Directors, Executive Officers and Employees \| 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
Directors, Executive Officers and Employees \| 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
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
2019 Plan
Subsidiary, Sale of Stock [Line Items]
Common stock available for future grant (in shares)								868,432
Total common shares reserved for future issuance (in shares)								6,847,361
Number of additional shares authorized (in shares)		4,166,860
Number of additional shares authorized yearly increase		5.00%