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Stockholders' Equity - Common Stock (Details) - USD ($) |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 16 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 21, 2018 | Jul. 25, 2018 | Jun. 01, 2018 | Oct. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | May 24, 2018 | May 23, 2018
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 6,723 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  | 50 |  |  |  |  |  |  | 50 |  | 50 | 2,300,000 | 23,400,000
Exercise of warrants |  |  |  |  | 490 |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net of offering cost |  |  |  |  |  |  |  |  |  |  |  | $ 15,964,000 | $ 6,246,000 |  |  |
Common stock issued, value |  |  |  |  |  | $ 64,000 | $ 1,873,000 |  | $ 3,686,000 | $ (297,000) | $ 27,000 |  |  |  |  |
Series U Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  |  | 3,450,000 |  |  |  |
Sale of Stock, Price Per Share |  |  |  |  | $ 5.00 |  |  |  |  |  |  | $ 5.00 |  | $ 5.00 |  |
Warrants expected term |  |  |  |  | 5 years |  |  |  |  |  |  | 5 years |  | 5 years |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 6,723 |  |  |  | 5,000 | 139,855 |  | 29,407 | 192 | 202 |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 141,183 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise of warrants |  |  |  | 1,039,000 |  |  |  |  |  |  |  | 1,672,000 |  |  |  |
Warrants expected term |  |  |  |  | 5 years |  |  |  |  |  |  | 5 years |  | 5 years |  |
Warrant exercise price |  | $ 39.93 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | B. Riley FBR [Member] | Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining availability under financing facility |  |  |  |  | $ 0 |  |  |  |  |  |  | $ 0 |  | $ 0 |  |
Common Stock [Member] | B. Riley FBR [Member] | Sales Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net of offering cost |  |  | $ 6,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | B. Riley FBR [Member] | ATM Program [Member] | Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  |
Proceeds from sale of common stock, net of offering cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,800,000 |  |
Remaining availability under financing facility |  |  |  |  | $ 0 |  |  |  |  |  |  | $ 0 |  | $ 0 |  |
Common Stock [Member] | B. Riley FBR [Member] | ATM Program [Member] | Sales Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net of offering cost |  |  | $ 6,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  |  | 32,170 |  |  |  |
Proceeds from sale of common stock, net of offering cost |  |  |  |  |  |  |  |  |  |  |  | $ 300,000 |  |  |  |
Common stock issued, value | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period exercisable from the date of issuance | 24 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] | Securities Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Trading Volume of Common Shares | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upper Limit on the Price Per Share | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining availability under financing facility | $ 100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beneficial ownership percentage of common stock outstanding | 4.99% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member] | Single Regular Purchase [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | 5,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] | Minimum [Member] | Single Regular Purchase [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] | Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  | 12,802 |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net of offering cost |  |  |  |  |  |  |  | $ 300,000 |  |  |  |  |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] | Purchase Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Floor price of per share | $ 12.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Series U Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  | 75,000 |  |  |  |  |  |  | 75,000 |  | 75,000 |  |
Warrant exercise price |  |  |  |  | $ 6.25 |  |  |  |  |  |  | $ 6.25 |  | $ 6.25 |  |
Common Class A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  |  | 289,000 |  |  |  |
Common Class B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  | 2,711,000 |  |  |  |  |  |  | 2,711,000 |  | 2,711,000 |  |

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