Basis of Presentation and Significant Accounting Policies - Purchase of Rights to Future Milestones, Royalties, and Commercial Payments (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Basis of Presentation and Significant Accounting Policies
Purchased receivables included in royalty and commercial payment receivables, Effective interest rate method	$ 27.2	$ 19.8
Purchased receivables included in royalty and commercial payment receivables, Cost recovery method	$ 2.6	$ 1.3

Amount, after allowance, of receivables related to income from purchased receivables under the effective interest rate method due within one year or the normal operating cycle, if longer.

No definition available.

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