Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements, Warrant Liabilities, Changes in Level 3, and Outstanding Debt (Details)

v2.4.1.9
Fair Value Measurements, Warrant Liabilities, Changes in Level 3, and Outstanding Debt (Details) (USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Reclassification of contingent warrant liability to equity upon exercise of warrants $ 0xoma_ReclassificationOfContingentWarrantLiabilityToEquityExerciseOfWarrants $ (2,525,000)xoma_ReclassificationOfContingentWarrantLiabilityToEquityExerciseOfWarrants  
Carrying Value [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Outstanding debt 47,189,000us-gaap_DebtInstrumentFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
  35,308,000us-gaap_DebtInstrumentFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Fair Value [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Outstanding debt 47,668,000us-gaap_DebtInstrumentFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
  36,461,000us-gaap_DebtInstrumentFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Warrant Liabilities [Member]      
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Risk-free interest rate (in hundredths) 0.55%us-gaap_FairValueAssumptionsRiskFreeInterestRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
   
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Beginning balance 31,828,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
69,869,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
69,869,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
Reclassification of contingent warrant liability to equity upon exercise of warrants 0xoma_ReclassificationOfContingentWarrantLiabilityToEquityExerciseOfWarrants
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
(2,525,000)xoma_ReclassificationOfContingentWarrantLiabilityToEquityExerciseOfWarrants
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
 
Net increase (decrease) in estimated fair value of contingent warrant liabilities upon revaluation 40,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
(20,002,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
 
Ending balance 31,868,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
47,342,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
 
Warrant Liabilities [Member] | Minimum [Member]      
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Expected volatility (in hundredths) 73.90%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
  69.60%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Risk-free interest rate (in hundredths)     0.03%us-gaap_FairValueAssumptionsRiskFreeInterestRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Expected term 1 year 8 months 8 days   0 years 1 month 2 days
Warrant Liabilities [Member] | Maximum [Member]      
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Expected volatility (in hundredths) 74.80%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
  72.90%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Risk-free interest rate (in hundredths)     0.67%us-gaap_FairValueAssumptionsRiskFreeInterestRate
/ us-gaap_FairValueByLiabilityClassAxis
= xoma_ContingentWarrantLiabilitiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Expected term 1 year 11 months 8 days   2 years 2 months 8 days
Foreign Exchange Option [Member] | Maximum [Member]      
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Estimated fair value of the foreign exchange options $ 100us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeOptionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember