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Basis of Presentation and Summary of Significant Accounting Policies - Financial Instruments (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Nov. 25, 2019 | Jun. 30, 2021 | Jan. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Amount paid for clearing fees |  | $ 19 | $ 231 |  |  |  |  |
Offering costs paid on the issuance of common stock and warrants |  |  |  | $ 1 | $ 0 | $ 470 | $ 474 | $ 510
Proceeds from sale of common stock and warrants |  | $ 4,500 | $ 2,300 |  |  |  |  |
Warrants issued (in shares) |  |  |  |  |  | 310,860 | 539,152 |
Exercise price of common stock (USD per share) |  |  |  | $ 3.59 |  | $ 3.59 |  |
Percentage of gross proceeds used to make payments on note |  |  | 10.00% |  |  |  |  |
Gross proceeds |  |  | $ 275 |  |  |  |  |
Payments on the Iliad Note |  |  |  | $ 0 | 450 | $ 0 | $ 976 |
Proceeds from issuance of warrants |  |  |  |  |  | $ 1,100 |  |
Warrants exercised (in shares) |  |  |  |  |  | 156,446 |  |
Proceeds from the exercise of warrants |  |  |  | $ 0 | $ 625 | $ 527 | $ 676 |
Iliad Note |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Percentage of gross proceeds used to make payments on note | 10.00% |  |  |  |  |  |  |
Payments on the Iliad Note |  |  | $ 226 |  |  |  |  |
Institutional investors |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Sale of common stock (in shares) |  | 990,100 | 688,360 |  |  |  |  |
Sale of common stock (USD per share) |  | $ 5.05 | $ 3.37 |  |  |  |  |
Warrants issued (in shares) |  |  | 688,360 |  |  | 269,180 | 497,472 |
Exercise price of common stock (USD per share) |  |  | $ 3.37 | $ 3.3700 | $ 3.3700 | $ 3.3700 | $ 3.3700 |
Purchase price (USD per share) |  |  | $ 0.625 |  |  |  |  |
Placement agent |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Amount paid for placement agent commissions |  | $ 400 | $ 193 |  |  |  |  |
Amount paid related to expenses for registered direct offering and concurrent private placement |  | $ 51 | $ 50 |  |  |  |  |
Warrants issued (in shares) |  |  | 48,185 |  |  | 41,680 | 41,680 |
Exercise price of common stock (USD per share) |  |  | $ 4.99 | $ 4.9940 | $ 4.9940 | $ 4.9940 | $ 4.9940 |

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