XML 43 R31.htm IDEA: XBRL DOCUMENT
v3.19.1

Condensed Consolidated Financial Statements Details - Additional Information (Details) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018
Long-term Equity Securities [Line Items] |  |  |  |
Long-term equity securities | $ 1,107,000 |  | $ 392,000 | [1]
Gain (loss) recognized due to change in fair value of investment | 715,000 |  |  |
Rezolute [Member] |  |  |  |
Long-term Equity Securities [Line Items] |  |  |  |
Long-term equity securities | 1,100,000 |  | $ 400,000 |
Gain (loss) recognized due to change in fair value of investment | $ 700,000 | $ 0 |  |
[1] | The condensed consolidated balance sheet as of December 31, 2018 has been derived from the audited consolidated financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.

X
- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714 + Details
Name: | us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Equity securities FvNi non current. + References No definition available. + Details
Name: | xoma_EquitySecuritiesFvNiNonCurrent
Namespace Prefix: | xoma_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Long term equity securities. + References No definition available. + Details
Name: | xoma_LongTermEquitySecuritiesLineItems
Namespace Prefix: | xoma_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=xoma_RezoluteIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |