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Summary of Significant Accounting Policies (Details 3) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Research and Development Expense [Abstract]      
Research and Development Expense $ 18,516,000us-gaap_ResearchAndDevelopmentExpense $ 17,000,000us-gaap_ResearchAndDevelopmentExpense $ 12,668,000us-gaap_ResearchAndDevelopmentExpense
Concentrations of Risk      
Amounts on deposit in excess of federally insured limits approximately $ 54,000,000xncr_DepositInExcessOfFederallyInsuredLimits $ 77,500,000xncr_DepositInExcessOfFederallyInsuredLimits  
Payables | Service providers      
Concentrations of risk      
Number of service providers 1xncr_NumberOfServiceProviders
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsPayableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_SupplierConcentrationRiskMember
5xncr_NumberOfServiceProviders
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsPayableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_SupplierConcentrationRiskMember
 
Concentration risk percentage 47.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsPayableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_SupplierConcentrationRiskMember
57.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsPayableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_SupplierConcentrationRiskMember