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Capital Stock - Rights Offerring 2018 - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions | 1 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Dec. 31, 2018 | Feb. 28, 2017 | Mar. 31, 2019 | Mar. 31, 2018 | Nov. 19, 2018
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Aggregate gross proceeds from issuance of common stock and preferred stock | $ 20.0 |  |  |  |
Offering costs offset against proceeds sale of common stock and preferred stock | 0.3 |  |  |  |
Net proceeds from issuance of common stock and preferred stock | $ 19.7 |  |  |  |
Preferred stock, stated value | $ 0.05 |  | $ 0.05 |  |
BVF [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Ownership percentage on outstanding shares |  |  | 19.99% |  |
Ownership percentage on outstanding shares |  |  | 53.40% |  |
Series Y Preferred Stock [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Total number of shares issued | 1,252.772 |  |  |  |
Series Y Convertible Preferred Stock [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Preferred stock, stated value | $ 13,000 |  |  |  |
Conversion of preferred stock into registered common stock | 1,000 |  |  |  |
Preferred stock conversion price per share | $ 13.00 |  |  |  |
Total number of shares of common stock issued upon conversion | 1,252,772 |  |  |  |
Percentage of convertible preferred stock conversion blocker provision | 19.99% |  |  |  |
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 |  |  |  |
Preferred shares converted |  |  | 0 |  |
Common Stock [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Total number of shares issued | 285,689 | 1,200,000 |  | 68,000 |
Common Stock [Member] | Series X Preferred Stock [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Rights offering amount |  |  |  |  | $ 20.0

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