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Stockholders' Equity - Preferred Stock (Details) - USD ($) |  |  |  |  | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 25, 2018 | Jul. 17, 2018 | Nov. 28, 2017 | Nov. 02, 2017 | Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | May 24, 2018 | May 23, 2018 | Nov. 27, 2017
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) |  |  |  |  | 5,000,000 |  | 5,000,000 | 5,000,000 | 5,000,000 | 5,000,000 |
Preferred stock, par value (in dollars per share) |  |  |  |  | $ 0.001 |  | $ 0.001 | $ 0.001 |  |  |
Preferred stock, shares issued (in shares) |  |  |  |  | 30,223 |  | 30,223 | 30,223 |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  |  | 4,540 |  | 4,606 | 2,431 |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  |  |  |  |  | 2,300,000 | 23,400,000 |
Common stock issued (in shares) | 6,723 |  | 10,000 |  |  |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) | 50 |  | 36,000 |  |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) | $ 39.93 |  | $ 166.65 |  |  |  |  |  |  |  |
Common stock issued (in shares) | 6,723 |  | 10,000 |  | 139,855 | 201 | 92,169 | 24,474 |  |  |
2017 Rights Offering [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Charge on Non Transferable Subscription Rights |  |  |  | $ 0 |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 10,000 |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) |  |  |  | $ 3.333 |  |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  |  |  |  | 30 months |  |  |  |
Common stock issued (in shares) |  |  | 10,000 |  |  |  |  |  |  |  |
Gross proceeds from private placement of stock |  |  | $ 8,800,000 |  |  |  |  |  |  |  |
Redemption price of warrant prior to expiration |  |  |  |  |  |  | $ 0.01 |  |  |  |
Common stock price per share for warrant redemption |  |  |  |  |  |  | $ 8.33 |  |  |  |
Number of consecutive trading days for warrant redemption |  |  |  |  |  |  | 10 days |  |  |  |
2017 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 18,000,000 |  |  |  |  |  |  |
Number of warrants exercisable |  |  |  | 10 |  |  |  |  |  |  |
2017 Rights Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 1 |  |  |  |  |  |  |
2018 Rights Offering [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 1 |  |  |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) |  | $ 39.93 |  |  |  |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  |  | 30 months |  | 30 months |  |  |  |
Common stock issued (in shares) | 6,723 |  |  |  |  |  |  |  |  |  |
Gross proceeds from private placement of stock | $ 5,700,000 |  |  |  |  |  |  |  |  |  |
Redemption price of warrant prior to expiration |  |  |  |  | $ 0.50 |  | $ 0.50 |  |  |  |
Common stock price per share for warrant redemption |  |  |  |  | $ 181.50 |  | $ 181.50 |  |  |  |
Number of consecutive trading days for warrant redemption |  |  |  |  | 20 days |  | 20 days |  |  |  |
Warrants liability fair value | $ 3,100,000 |  |  |  | $ 1,500,000 |  | $ 900,000 |  |  |  |
2018 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 1,050 |  |  |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) |  | $ 1,000 |  |  |  |  |  |  |  |  |
2018 Rights Offering [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) | 141,183 | 141,183 |  |  |  |  |  |  |  |  |
Series A Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares issued (in shares) |  |  |  |  | 13,500 |  | 13,500 | 13,500 |  |  |
Convertible preferred stock |  |  |  |  | 3.60% |  | 3.60% | 3.60% |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  |  | 0 |  | 0 | 0 |  |  |
Series B Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) |  |  |  |  |  |  |  |  |  |  | 10,000
Preferred stock, par value (in dollars per share) |  |  |  |  |  |  |  |  |  |  | $ 0.001
Preferred stock, shares issued (in shares) |  |  |  |  | 10,000 |  | 10,000 | 10,000 |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  |  | 1,112 |  | 1,112 | 2,431 |  |  |
Number of shares callable by warrants (in shares) |  |  | 360,000 |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  | 60,000 |  |  |  |  |  |  |  |
Series B Convertible Preferred Stock [Member] | 2017 Rights Offering [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  | 10,000 |  |  |  |  |  |  |
Series C Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) | 7,000 |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) | $ 0.001 |  |  |  |  |  |  |  |  |  |
Preferred stock, shares issued (in shares) |  |  |  |  | 6,723 |  | 6,723 |  |  |  |
Preferred stock, shares outstanding (in shares) |  |  |  |  | 3,428 |  | 3,494 | 0 |  |  |
Number of shares callable by warrants (in shares) | 7,059,150 |  |  |  |  |  |  |  |  |  |
Number of share converted into common stock for each share (in shares) | 25 |  |  |  |  |  |  |  |  |  |
Series C Convertible Preferred Stock [Member] | Dividend Paid [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dividends payable |  |  |  |  |  |  | $ 2,500,000 |  |  |  |
Series C Convertible Preferred Stock [Member] | 2018 Rights Offering [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  | 20,000 |  |  |  |  |  |  |  |  |
Common Stock and Series B Convertible Preferred Stock [Member] | 2018 Rights Offering [Member] |  |  |  |  |  |  |  |  |  |  |
Preferred Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |
Charge on Non Transferable Subscription Rights |  | $ 0 |  |  |  |  |  |  |  |  |

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