Subsequent Events (Details)	1 Months Ended
Apr. 30, 2022
Subsequent Event \| Thomas Burns, Senior Vice President of Finance and Chief Financial Officer
Subsequent Event
Continued employment period to be deemed "retirement eligible" for purposes of equity award agreements	12 months

Period over which employee must remain employed following event as described in agreement to be deemed "retirement eligible" for purposes of equity award agreements, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days

No definition available.

Name:	xoma_EmploymentAgreementAmendmentEquityAwardEligibilityEmploymentPeriod
Namespace Prefix:	xoma_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration