Lease Agreements - Leased facilities (Details) - Leased facilities, Emeryville, California $ in Thousands	12 Months Ended
Dec. 31, 2022 USD ($) facility
Leases
Operating leases, number of leased facilities \| facility	1
Net lease liability until expiration of lease \| $	$ 34

Amount of lessee's net lease liability until expiration of operating lease to be paid in next fiscal year following current fiscal year. Excludes payments after extension of lease.

No definition available.

Name:	xoma_LesseeOperatingLeaseLiabilityToBePaidYearOnePriorToExpirationOfLease
Namespace Prefix:	xoma_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant