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Subsequent events - Additional Information (Details) |  |  | 9 Months Ended |  |
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Oct. 17, 2016 | Oct. 14, 2016 | Sep. 30, 2016 | Oct. 31, 2016 $ / shares | Mar. 15, 2016 $ / shares
Subsequent Event [Line Items] |  |  |  |  |
Reverse stock split, description |  |  | In October 2016, the Company’s stockholders voted at a special meeting of stock holders to approve a series of alternate amendments to the Company’s Amended Certificate of Incorporation to effect a reverse stock split of the Company’s issued and outstanding common stock. The Company’s Board of Directors then approved a specific ratio of 1-for-20. |  |
Subsequent Event [Member] |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Minimum bid price requirement of common stock |  |  |  | $ 1.00 |
Reverse stock split, description | Upon the effectiveness of the reverse stock split, (i) every 20 shares of the Company’s outstanding common stock was combined into 1 share of common stock, (ii) the number of shares of common stock available for issuance under the 2010 Plan and ESPP was proportionally decreased, (iii) the number of shares of common stock issuable upon the exercise of the outstanding stock options and warrants was proportionally decreased, (iv) the exercise price of the outstanding stock options and warrants was proportionally increased, and (v) the number of shares of common stock issuable upon the vesting of the outstanding restricted stock units was proportionally decreased. The par value per share and the authorized number of shares of common stock and preferred stock were not adjusted as a result of the reverse stock split. | At a special meeting held on October 14, 2016, XOMA’s stockholders approved the reverse stock split and gave XOMA’s Board of Directors’ discretion to effect the reverse split within a range of ratios. The Board subsequently decided to effect a reverse stock split in a ratio of 1-for-20, effective after market close on October 17, 2016. |  |  |
Reverse stock split ratio | 0.05 |  |  |  |
NASDAQ Stock Market LLC [Member] |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Minimum bid price requirement of common stock |  |  |  |  | $ 1.00

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- Definition Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB TOPIC 4.C) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Stock Split -URI http://asc.fasb.org/extlink&oid=6525746 + Details
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- Definition Description of the reverse stock split arrangement. Also provide the retroactive effect given by the reverse split that occurs after the balance sheet date but before the release of financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 4.C) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770 + Details
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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
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- Definition Minimum bid price requirement. + References No definition available. + Details
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- Details
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- Details
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