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Stockholders' Equity - Warrants (Details) - USD ($) |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Jul. 25, 2018 | Jul. 17, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Apr. 30, 2020
Preferred Stock [Abstract] |  |  |  |  |
Warrant exercise price (in dollars per share) |  |  | $ 2.25 |  |
Warrant liability |  |  | $ 7,000 | $ 6,929,000 |
Change in fair value of warrants |  |  | (2,400,000) | $ (3,407,000) |
Outstanding Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Warrant liability |  |  | 4,500,000 |  |
Change in fair value of warrants |  |  | $ 700,000 |  |
Series U Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Common stock issued (in shares) |  |  | 3,450,000 |  |
Sale of Stock, Price Per Share |  |  | $ 5.00 |  |
Warrants expected term |  |  | 5 years |  |
Representative Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  |  | 75,000 |  |
Warrant exercise price (in dollars per share) |  |  | $ 6.25 |  |
Warrant exercise price decrease |  |  | $ 2.81 |  |
Common Stock [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Common stock issued (in shares) |  |  |  | 184,666 |
Warrants expected term |  |  | 5 years |  |
Series C Convertible Preferred Stock [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Warrant exercise price (in dollars per share) |  |  |  |  | $ 2.25
Common Class A [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Common stock issued (in shares) |  |  | 289,000 |  |
Common Class B [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  |  | 2,711,000 |  |
2018 Rights Offering [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  | 1 |  |  |
Common stock issued (in shares) | 6,723 |  |  |  |
Gross proceeds from private placement of stock | $ 5,700,000 |  |  |  |
2018 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  | 1,050 |  |  |
2018 Rights Offering [Member] | Common Stock and Series B Convertible Preferred Stock [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Charge on Non Transferable Subscription Rights |  | $ 0 |  |  |
2018 Rights Offering [Member] | Series C Convertible Preferred Stock [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  | 20,000 |  |  |
2018 Rights Offering [Member] | Series C Convertible Preferred Stock [Member] | Outstanding Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Warrant exercise price (in dollars per share) |  | $ 1,000 |  |  |
2018 Rights Offering [Member] | Common Stock [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  |  |  |  | 1
2018 Rights Offering [Member] | Common Stock [Member] | Outstanding Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  |  |  |  | 50
Series T Warrants [Member] | 2018 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Class of warrant outstanding |  |  | 3,787,350 |  |
Number of warrants exercised |  |  | 75,747 |  |
Series U Warrants [Member] | Outstanding Warrants [Member] |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |
Number of securities called by warrant or right |  |  | 3,447,500 |  |
Class of warrant outstanding |  |  | 3,037,500 |  |
Number of warrants exercised |  |  | 3,037,500 |  |

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