v3.3.1.900
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2015
Mar. 07, 2016
Jun. 30, 2015
Document And Entity Information [Abstract]      
Entity Registrant Name XOMA Corp    
Entity Central Index Key 0000791908    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Accelerated Filer    
Entity Public Float     $ 451,024,815
Entity Common Stock, Shares Outstanding   119,615,729  
Document Fiscal Year Focus 2015    
Document Fiscal Period Focus FY    
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2015