Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 808
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479402/808-10-50-1

+ Details

Name:	us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of deferred income excluding obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as current.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 25
-Paragraph 2
-SubTopic 10
-Topic 470
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481174/470-10-25-2

+ Details

Name:	us-gaap_DeferredIncomeCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of deferred income excluding obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as noncurrent.

+ References

+ Details

Name:	us-gaap_DeferredIncomeNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase (decrease) in deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

+ Details

Name:	us-gaap_IncreaseDecreaseInDeferredRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of arranger fee receivable for the acquisition related services rendered.

+ References

No definition available.

+ Details

Name:	xoma_AcquisitionServiceArrangerFeeReceivable
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of agreements.

+ References

No definition available.

+ Details

Name:	xoma_AgreementsNumber
Namespace Prefix:	xoma_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Eligible potential additional payments receivable upon achievement of specified future net sales milestones.

+ References

No definition available.

+ Details

Name:	xoma_EligiblePotentialAdditionalPaymentsReceivableUponAchievementOfSpecifiedFutureNetSalesMilestones
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of milestone periods for which entity is eligible to receive payments upon achievement of milestone.

+ References

No definition available.

+ Details

Name:	xoma_MilestonePeriodsNumber
Namespace Prefix:	xoma_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Payment for Short-term Loan to Acquirer, Other Arrangement, Structuring Agent, Acquisition, Investing Activity

+ References

No definition available.

+ Details

Name:	xoma_PaymentForShortTermLoanToAcquirerOtherArrangementStructuringAgentAcquisitionInvestingActivity
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cash proceeds received under agreement. May include, but is not limited to, upfront payments, one-time payments and cash-portion of payments received.

+ References

No definition available.

+ Details

Name:	xoma_ProceedsFromUpfrontPayment
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Repayment of Short-term Loan to Acquirer, Other Arrangement, Structuring Agent, Acquisition, Investing Activity

+ References

No definition available.

+ Details

Name:	xoma_RepaymentOfShortTermLoanToAcquirerOtherArrangementStructuringAgentAcquisitionInvestingActivity
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue that is not accounted for under Topic 606, in accordance with the units-of-revenue method.

+ References

No definition available.

+ Details

Name:	xoma_RevenueNotFromContractWithCustomerUnitsOfRevenueMethod
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_OwnershipAxis=xoma_EssaPharmaIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=xoma_BiotechnologyValueFundLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_InvestorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=xoma_HealthCareRoyaltyPartnersTwoLimitedPartnersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=xoma_RoyaltyInterestAcquisitionAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=xoma_FirstRoyaltyInterestAcquisitionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=xoma_SecondRoyaltyInterestAcquisitionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=xoma_XenotherapeuticsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

License, Collaboration, and Other Arrangements - ESSA arrangement and Sale of Future Revenue Streams (Details) $ in Thousands			12 Months Ended
	Oct. 09, 2025 USD ($)	Dec. 21, 2016 USD ($) agreement period	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Oct. 31, 2025 USD ($)	Oct. 08, 2025
Acquisitions, Licensing and Other Arrangements
Payment to issue short-term loan to Xeno			$ 5,877
Receipt from short-term loan repayment by Xeno			5,877
Unearned revenue recognized under units-of-revenue method			(1,310)	$ (3,570)
Revenue recognized under units-of-revenue method			1,310	3,570
Unearned revenue recognized under units-of-revenue method, current			1,268	1,361
Unearned revenue recognized under units-of-revenue method, noncurrent			3,193	4,410
Essa Pharma Inc \| BVF \| Investor
Acquisitions, Licensing and Other Arrangements
Ownership interest (as a percent)						24.70%
HealthCare Royalty Partners II, L.P. \| Royalty Sale Agreements
Acquisitions, Licensing and Other Arrangements
Number of agreements \| agreement		2
Unearned revenue recognized under units-of-revenue method		$ 18,000
Revenue recognized under units-of-revenue method			1,300	3,600
Unearned revenue recognized under units-of-revenue method, current			1,300	1,400
Unearned revenue recognized under units-of-revenue method, noncurrent			$ 3,200	$ 4,400
HealthCare Royalty Partners II, L.P. \| First Royalty Sale Agreement
Acquisitions, Licensing and Other Arrangements
Cash payment received		6,500
Eligible potential additional payments receivable upon achievement of specified net sales milestones in future years		$ 4,000
Number of milestone periods \| period		3
HealthCare Royalty Partners II, L.P. \| Second Royalty Sale Agreement
Acquisitions, Licensing and Other Arrangements
Cash payment received		$ 11,500
Xeno
Acquisitions, Licensing and Other Arrangements
Acquisition service, arranger fee, receivable					$ 3,000
Payment to issue short-term loan to Xeno	$ 5,900
Receipt from short-term loan repayment by Xeno	$ 5,900