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Stockholders' Equity - Narrative (Details) - USD ($) |  |  |  |  |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 16, 2018 | May 01, 2018 | Mar. 09, 2018 | Mar. 07, 2018 | Dec. 29, 2017 | Sep. 30, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | May 31, 2018
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) |  |  |  |  |  |  | 5,000,000 | 5,000,000 |
Preferred stock, par value (usd per share) |  |  |  |  |  |  | $ 0.0001 | $ 0.0001 |
Preferred stock, shares issued (in shares) |  |  |  |  |  |  | 0 | 0 |
Warrants issued (in shares) | 11,520,000 |  |  |  | 316,163 |  |  |  |
Proceeds from issuance of preferred stock, preference stock, and warrants |  |  |  |  |  |  | $ 9,647,000 | $ 0 |
Shares issued upon conversion (in shares) | 3,748,184 |  |  |  |  |  |  |  |
Convertible preferred stock converted to other securities | $ 7,871,186 |  |  |  |  |  |  |  |
Exercise price (usd per share) | $ 2.10 |  |  |  | $ 7.42 |  |  |  | $ 6.59
Warrant term | 5 years |  |  |  | 5 years |  |  |  |
Deemed dividend arising from the issuance of common stock to Series A convertible preferred stockholders under most favored nation provision |  |  |  |  |  | $ 8,700,000 | 8,654,000 | 0 |
Increase (decrease) in fair value of warrant liability |  |  |  |  |  |  | $ 491,000 | $ 0 |
Common stock, shares authorized (in shares) |  |  |  |  |  |  | 350,000,000 | 350,000,000 |
Common stock, par value (usd per share) |  |  |  |  |  |  | $ 0.0001 | $ 0.0001 |
Sale of stock, price per share (in usd per share) | $ 2.10 |  |  |  |  |  |  |  |
Common stock warrant, shares to purchase | 1 |  |  |  |  |  |  |  |
Exercise price (usd per share) | $ 0.0001 |  |  |  |  |  |  |  |
Sale of stock, consideration received on transaction | $ 21,600,000 |  |  |  |  |  |  |  |
Purchase Agreement | Private Placement First Closing |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Warrants issued shares (in shares) |  |  | 774,186 |  |  |  |  |  |
Series A Non-voting Convertible | Purchase Agreement |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Preferred stock, par value (usd per share) |  |  |  | $ 0.0001 |  |  |  |  |
Preferred stock, shares issued (in shares) |  |  |  | 10,700 |  |  |  |  |
Warrants issued (in shares) |  |  |  | 1,383,631 |  |  |  |  |
Proceeds from issuance of preferred stock, preference stock, and warrants |  |  |  | $ 10,700,000 |  |  |  |  |
Shares issued upon conversion (in shares) |  |  |  | 1,844,835 |  |  |  |  |
Conversion price (USD per share) |  |  |  |  |  |  | $ 1.00 |  |
Warrant term |  |  |  | 5 years 6 months |  |  |  |  |
Series A- Convertible Preferred Stock | Private Placement First Closing |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Deemed dividend on beneficial conversion feature of convertible preferred stock |  | $ 2,500,000 | $ 2,000,000 |  |  |  |  |  |
Series A- Convertible Preferred Stock | Purchase Agreement |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Conversion price (USD per share) |  |  | $ 5.80 | $ 6.59 |  |  |  |  |
Series A- Convertible Preferred Stock | Purchase Agreement | Private Placement First Closing |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from issuance of preferred stock, preference stock, and warrants |  |  | $ 6,000,000 |  |  |  |  |  |
Convertible preferred stock issued shares (in shares) |  |  | 5,987 |  |  |  |  |  |
Series A- Convertible Preferred Stock | Purchase Agreement | Private Placement Second Closing |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from issuance of preferred stock, preference stock, and warrants |  |  | $ 4,700,000 |  |  |  |  |  |
Convertible preferred stock issued shares (in shares) |  |  | 4,713 |  |  |  |  |  |
Warrants issued shares (in shares) |  |  | 609,445 |  |  |  |  |  |
Warrant |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Shares issued upon conversion (in shares) | 3,748,184 |  |  |  |  |  |  |  |
Warrant term | 5 years |  |  |  |  |  |  |  |
Sale of stock, number of shares issued in transaction | 4,675,000 |  |  |  |  |  |  |  |
Sale of stock, price per share (in usd per share) | $ 2.0999 |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Warrant term | 5 years |  |  |  |  |  |  |  |
Sale of stock, number of shares issued in transaction | 6,845,000 |  |  |  |  |  |  |  |

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