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Loans - Additional Information (Detail) (USD $)
 3 Months Ended
Mar. 31, 2015
Item
Mar. 31, 2014
Feb. 28, 2015
Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Maximum loan-to-value percentage on home equity loans 80.00%cfr_MaximumLoanToValuePercentageOnHomeEquityLoans      
Concentration of loans in a single industry in excess of ten percent 0.00%cfr_Concentrationofloansinasingleindustryinexcessoftenpercent      
Maximum percentage loan related to single industry 10.00%cfr_MaximumPercentageOfLoanRelatedToSingleIndustry      
Minimum number of days to be considered past due 90 days      
Troubled debt restructurings $ 613,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 $ 793,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2    
Previously restructured loans past due 0cfr_PreviouslyRestructuredLoansPastDue      
Financing receivable, modifications, pre-modification recorded investment 709,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 819,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2    
Number of days past due for payment of interest on loans, minimum 120 days      
Number of loans with calculated risk of 10 or higher greater than $5 million 3cfr_NumberOfLoansWithCalculatedRiskOfTenOrHigher      
Loan amount threshold 5,000,000cfr_LoanAmountThreshold      
Loan value with weighted-average loan-to-value 33,200,000cfr_LoanValueWithWeightedAverageLoanToValue      
Weighted-average loan-to-value ratio 64.20%cfr_WeightedAverageLoanToValueRatioPercentage      
Texas Leading Index economic condition indicator     126.9cfr_TexasLeadingIndexEconomicConditionIndicator 129.4cfr_TexasLeadingIndexEconomicConditionIndicator
Maximum origination value of loans which were subject to further refinement of valuation methodology 1,000,000cfr_MaximumOriginationValueOfLoansWhichWereSubjectToFurtherRefinementOfValuationMethodology      
Commercial Real Estate Portfolio Segment [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Percentage of owner-occupied commercial real estate loans 54.00%cfr_PercentageOfOwnerOccupiedCommercialRealEstateLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		      
Commercial and industrial, Energy [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Percentage of loans related to a single industry 16.20%cfr_Percentageofloansrelatedtoasingleindustry
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		      
Troubled debt restructurings 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		    
Financing receivable, modifications, pre-modification recorded investment 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		    
Non-Accrual Loans [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Additional interest that would have been recognized on non-accrual loans, net of tax 397,000us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_NonAccrualLoansMember		 358,000us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_NonAccrualLoansMember		    
Commercial Portfolio Segment [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Financing receivables, impaired, troubled debt restructuring, write-down 88,000us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember		      
Financing receivable, modifications, pre-modification recorded investment 314,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember		      
Number of days past due for payment of interest on loans, minimum 180 days      
Grade 12 [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Number of days past due for payment of interest on loans, minimum 120 days      
General percentage of valuation allowance in excess of principal balance, maximum 30.00%cfr_PercentOfValuationAllowanceInExcessOfPrincipalBalanceMaximum
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_GradeTwelveMember		      
Grade 13 [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
General percentage of valuation allowance in excess of principal balance, minimum 30.00%cfr_PercentOfValuationAllowanceInExcessOfPrincipalBalanceMinimum
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_GradeThirteenMember		      
Commercial real estate, Buildings, land and other [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Previously Restructured Loans Moved to OREO 500,000cfr_PreviouslyRestructuredLoansMovedtoOREO
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		      
Charge-off of previously restructures loans $ 0cfr_ChargeOffOfPreviouslyRestructuresLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember