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Capital Stock - Rights Offering 2019 (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Dec. 02, 2019 | Dec. 31, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Feb. 29, 2020
Sale of stock |  |  |  |  |  |
Stock issuance costs |  |  | $ 231 | $ 377 |  |
Preferred stock, stated value (in dollars per share) |  | $ 0.05 | $ 0.05 |  | $ 0.05 |
Series Y Preferred Stock | BVF |  |  |  |  |  |
Sale of stock |  |  |  |  |  |
Beneficial ownership limitation (as a percent) |  |  |  |  |  | 50.00%
2019 Rights Offering |  |  |  |  |  |
Sale of stock |  |  |  |  |  |
Aggregate gross proceeds from issuance of common stock and preferred stock | $ 22,000 | $ 22,000 |  |  |  |
Stock issuance costs |  | 200 |  |  |  |
Net proceeds from issuance of stock |  | $ 21,800 |  |  |  |
2019 Rights Offering | BVF |  |  |  |  |  |
Sale of stock |  |  |  |  |  |
Legal fees and expenses |  |  |  |  | $ 18 |
2019 Rights Offering | Common Stock |  |  |  |  |  |
Sale of stock |  |  |  |  |  |
Total number of shares issued |  | 1,000,000 |  |  |  |
2019 Rights Offering | Common Stock | BVF |  |  |  |  |  |
Sale of stock |  |  |  |  |  |
Total number of shares issued |  | 845,463 |  |  |  |
Purchase price (in dollars per share) |  | $ 22.00 |  |  | $ 22.00 |
BVF | Common Stock | Xoma Corporation |  |  |  |  |  |
Sale of stock |  |  |  |  |  |
Ownership percentage on outstanding shares |  |  | 37.90% |  |  |
Ownership interest, if shares are converted (as a percent) |  |  | 57.30% |  |  |

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