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Capital Stock - Biotechnology Value Fund Financing 2017 - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Feb. 28, 2017 | Dec. 31, 2018 | Dec. 31, 2017
Class Of Warrant Or Right [Line Items] |  |  |  |
Cash proceeds from issuance of common stock and convertible preferred stock | $ 19.7 |  |  |
Preferred stock, stated value | $ 0.05 |  | $ 0.05 | $ 0.05
BVF [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Cash proceeds from issuance of common stock and convertible preferred stock |  | $ 24.8 |  |
Series X Convertible Preferred Stock [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Sale of shares |  | 5,003 |  |
Preferred stock, stated value |  | $ 4,030 |  |
Conversion of preferred stock into registered common stock |  | 1,000 |  |
Preferred stock conversion price per share | $ 4.03 | $ 4.03 | $ 4.03 |
Total number of shares of common stock issued upon conversion |  | 5,003,000 |  |
Percentage of convertible preferred stock conversion blocker provision |  | 19.99% |  |
Fair value of common stock amount exceeded purchase price of convertible preferred stock |  | $ 5.6 |  |
Series X and Series Y Convertible Preferred Stock [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Conversion of preferred stock into registered common stock | 1,000 |  | 1,000 |
Series Y Convertible Preferred Stock [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Preferred stock, stated value | $ 13,000 |  | $ 13,000 |
Conversion of preferred stock into registered common stock | 1,000 |  | 1,000 |
Preferred stock conversion price per share | $ 13.00 |  | $ 13.00 |
Total number of shares of common stock issued upon conversion | 1,252,772 |  | 1,252,772 |
Percentage of convertible preferred stock conversion blocker provision | 19.99% |  |  |
Common Stock [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Sale of shares | 285,689 | 1,200,000 | 354,000 | 1,849,000
Common stock share price |  | $ 4.03 |  |

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