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Stockholders' Equity - Warrants (Details) - USD ($) |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jul. 25, 2018 | Jul. 17, 2018 | Apr. 30, 2020 | Sep. 30, 2020 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) |  |  |  | $ 2.25 |  |  |  | $ 2.25 |  |
Warrant liability |  |  |  | $ 83,000 |  |  |  | $ 83,000 |  | $ 6,929,000
Change in fair value of warrants |  |  |  | 81,000 | $ 561,000 |  |  | (2,342,000) | $ 69,000 |
Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant liability |  |  |  | $ 4,500,000 |  |  |  | 4,500,000 |  |
Change in fair value of warrants |  |  |  |  |  |  |  | $ 700,000 |  |
Series U Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  | 3,450,000 |  |
Sale of Stock, Price Per Share |  |  |  | $ 5.00 |  |  |  | $ 5.00 |  |
Warrants expected term |  |  |  | 5 years |  |  |  | 5 years |  |
Representative Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 75,000 |  |  |  | 75,000 |  |
Warrant exercise price (in dollars per share) |  |  |  | $ 6.25 |  |  |  | $ 6.25 |  |
Warrant exercise price decrease |  |  |  |  |  |  |  | $ 2.81 |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  | 5,000,000 | 139,855,000 |  |  |
Warrants expected term |  |  |  | 5 years |  |  |  | 5 years |  |
Series C Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Conversion Price Per Share |  |  | $ 3.2132 |  |  |  |  |  |  |
Preferred stock conversion price reduced (in dollars per share) |  |  | $ 2.25 |  |  |  |  |  |  |
Common Class A |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  | 289,000 |  |
Common Class B |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 2,711,000 |  |  |  | 2,711,000 |  |
2018 Rights Offering [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 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] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 1,050 |  |  |  |  |  |  |  |
2018 Rights Offering [Member] | Common Stock and Series B Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Charge on Non Transferable Subscription Rights |  | $ 0 |  |  |  |  |  |  |  |
2018 Rights Offering [Member] | Series C Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 20,000 |  |  |  |  |  |  |  |
2018 Rights Offering [Member] | Series C Convertible Preferred Stock [Member] | Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) |  | $ 1,000 |  |  |  |  |  |  |  |
2018 Rights Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  | 1 |  |  |  |  |  |  |
2018 Rights Offering [Member] | Common Stock [Member] | Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  | 50 |  |  |  |  |  |  |
Series T Warrants [Member] | 2018 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Class of warrant outstanding |  |  |  | 3,787,350 |  |  |  | 3,787,350 |  |
Number of warrants exercised |  |  |  |  |  |  |  | 75,747 |  |
Series U Warrants [Member] | Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 3,447,500 |  |  |  | 3,447,500 |  |
Class of warrant outstanding |  |  |  | 3,045,000 |  |  |  | 3,045,000 |  |
Number of warrants exercised |  |  |  |  |  |  |  | 3,045,000 |  |

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