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Stockholders' Equity - Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Class of Stock [Line Items] |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) |  |  |  | $ 2.25 |  | $ 2.25 |
Warrant liability | $ 3 |  |  |  | $ 3 |  | $ 7
Change in fair value of warrants | $ (2) |  |  | $ 81 | $ (4) | $ (2,342) |
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 securities called by warrant or right | 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) | 3,272,500 | 1,907,000 | 2,534,879 |  |  |  |
Warrants expected term | 5 years |  |  |  | 5 years |  |
Outstanding Warrants [Member] |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Warrant liability |  |  |  | $ 4,500 |  | $ 4,500 |
Change in fair value of warrants |  |  |  |  |  | $ 700 |
Outstanding Warrants [Member] | Series U Warrants [Member] |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Number of securities called by warrant or right |  |  |  | 3,447,500 |  | 3,447,500 |
Class of warrant outstanding | 2,141,000 |  |  |  | 2,141,000 |  |
Number of warrants exercised |  |  |  |  | 2,141,000 |  |
Common Class A [Member] |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  | 289,000 |  |
Common Class B [Member] |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Number of securities called by warrant or right | 2,711,000 |  |  |  | 2,711,000 |  |

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