Commitments and Contingencies - Arbitration Proceeding (Details)	1 Months Ended
Jun. 30, 2021 item
Commitments and Contingencies
Number of arbitration proceedings initiated	1

Number of arbitration proceedings initiated by entity against one of its licensees.

No definition available.

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