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Other Borrowings (Narrative) (Details) (USD $)
12 Months Ended 9 Months Ended 1 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Sep. 30, 2013
Dec. 15, 2014
Nov. 06, 2014
Mar. 15, 2011
Dec. 31, 2010
Dec. 31, 2014
Nov. 30, 2013
Dec. 15, 2013
Dec. 07, 2010
Debt Instrument [Line Items]                        
Notes Payable $ 0us-gaap_NotesPayable $ 364,000us-gaap_NotesPayable             $ 0us-gaap_NotesPayable      
Debt Instrument, Frequency of Periodic Payment     annual                  
Loans Payable to Bank 150,000,000us-gaap_LoansPayableToBank     101,000,000us-gaap_LoansPayableToBank         150,000,000us-gaap_LoansPayableToBank      
Proceeds from (Repayments of) Other Debt (58,639,000)us-gaap_ProceedsFromRepaymentsOfOtherDebt (22,396,000)us-gaap_ProceedsFromRepaymentsOfOtherDebt (306,786,000)us-gaap_ProceedsFromRepaymentsOfOtherDebt                  
Securities sold under repurchase agreements 48,566,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase 235,347,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase             48,566,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase      
Net Credit Exposure Repurchase Agreements 0wtfc_NetCreditExposureRepurchaseAgreements               0wtfc_NetCreditExposureRepurchaseAgreements      
Other 18,822,000us-gaap_OtherLongTermDebt 19,393,000us-gaap_OtherLongTermDebt             18,822,000us-gaap_OtherLongTermDebt      
Secured Debt 129,077,000us-gaap_SecuredDebt 0us-gaap_SecuredDebt             129,077,000us-gaap_SecuredDebt      
Unsecured Debt [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Frequency of Periodic Payment quarterly                      
Subordinated Debt [Member]                        
Debt Instrument [Line Items]                        
Maturity date Jun. 13, 2024                      
Fixed interest rate 5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SubordinatedDebtMember
              5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SubordinatedDebtMember
     
Loans Payable [Member]                        
Debt Instrument [Line Items]                        
Notes Payable 0us-gaap_NotesPayable
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
0us-gaap_NotesPayable
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
            0us-gaap_NotesPayable
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LoansPayableMember
     
Debt Instrument, Issuance Date       Oct. 30, 2009                
Line of Credit [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Frequency of Periodic Payment quarterly                      
Line of Credit Facility, Maximum Borrowing Capacity       100,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
100,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
             
Maturity date   Oct. 25, 2013   Oct. 25, 2013 Dec. 15, 2014 Nov. 06, 2014            
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage 0.20%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_LineOfCreditMember
                     
Notes Payable to Banks [Member]                        
Debt Instrument [Line Items]                        
Loans Payable to Bank   1,000,000us-gaap_LoansPayableToBank
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
  1,000,000us-gaap_LoansPayableToBank
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
               
Maturity date Jun. 01, 2015                      
Proceeds from (Repayments of) Other Debt   (1,000,000)us-gaap_ProceedsFromRepaymentsOfOtherDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
                   
Revolving Credit Facility [Member]                        
Debt Instrument [Line Items]                        
Line of Credit Facility, Maximum Borrowing Capacity 75,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
              75,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
     
Maturity date Dec. 14, 2015                      
Term Facility [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Frequency of Periodic Payment quarterly                      
Loans Payable to Bank 75,000,000us-gaap_LoansPayableToBank
/ us-gaap_LongtermDebtTypeAxis
= wtfc_TermFacilityMember
              75,000,000us-gaap_LoansPayableToBank
/ us-gaap_LongtermDebtTypeAxis
= wtfc_TermFacilityMember
     
Maturity date Jun. 15, 2020                      
Debt Instrument, Date of First Required Payment Sep. 30, 2015                      
Loan Agreement [Member]                        
Debt Instrument [Line Items]                        
Notes Payable 0us-gaap_NotesPayable
/ us-gaap_LongtermDebtTypeAxis
= wtfc_LoanAgreementMember
              0us-gaap_NotesPayable
/ us-gaap_LongtermDebtTypeAxis
= wtfc_LoanAgreementMember
     
Master Repurchase Agreements [Member]                        
Debt Instrument [Line Items]                        
Securities sold under repurchase agreements 48,600,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember
55,300,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember
            48,600,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember
     
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements 62,500,000us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesForRepurchaseAgreements
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember
              62,500,000us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesForRepurchaseAgreements
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember
     
Banks And Brokers [Member]                        
Debt Instrument [Line Items]                        
Securities sold under repurchase agreements   180,000,000us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_LongtermDebtTypeAxis
= wtfc_BorrowingsFromBanksAndBrokersMember
                   
Fixed Rate Promissory Note [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Frequency of Periodic Payment monthly                      
Debt Instrument, Issuance Date Aug. 31, 2012                      
Maturity date Sep. 01, 2017                      
Other 18,800,000us-gaap_OtherLongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= wtfc_FixedRatePromissoryNoteMember
19,300,000us-gaap_OtherLongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= wtfc_FixedRatePromissoryNoteMember
            18,800,000us-gaap_OtherLongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= wtfc_FixedRatePromissoryNoteMember
     
Fixed interest rate 3.75%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= wtfc_FixedRatePromissoryNoteMember
              3.75%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= wtfc_FixedRatePromissoryNoteMember
     
Junior Subordinated Amortizing Notes [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Frequency of Periodic Payment   quarterly                    
Debt Instrument, Issuance Date Dec. 31, 2010                      
Maturity date   Dec. 15, 2013           Dec. 15, 2013        
Debt Instrument, Date of First Required Payment   Mar. 15, 2011                    
Fixed interest rate                     9.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= wtfc_JuniorSubordinatedAmortizingNotesMember
 
Junior subordinated notes                       44,700,000us-gaap_JuniorSubordinatedNotes
/ us-gaap_LongtermDebtTypeAxis
= wtfc_JuniorSubordinatedAmortizingNotesMember
Quarterly principal and interest payments   4,300,000us-gaap_DebtInstrumentPeriodicPayment
/ us-gaap_LongtermDebtTypeAxis
= wtfc_JuniorSubordinatedAmortizingNotesMember
                   
Debt Instrument, Initial Payment             4,600,000wtfc_DebtInstrumentInitialPayment
/ us-gaap_LongtermDebtTypeAxis
= wtfc_JuniorSubordinatedAmortizingNotesMember
         
Secured Debt [Member]                        
Debt Instrument [Line Items]                        
Fixed interest rate 1.7987%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
              1.7987%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
     
Proceeds from Issuance of Debt                 $ 150,000,000us-gaap_ProceedsFromIssuanceOfDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember
     
Federal Funds Rate [Member] | Unsecured Debt [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ us-gaap_VariableRateAxis
= wtfc_FederalFundsRateMember
                     
London Interbank Offered Rate (LIBOR) [Member] | Subordinated Debt [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate     1.30%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
            1.30%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
   
Base Rate Loan [Member] | Federal Funds Rate [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_BaseRateLoanMember
/ us-gaap_VariableRateAxis
= wtfc_FederalFundsRateMember
                     
Base Rate Loan [Member] | Highest Rate [Member] | Revolving Credit Facility [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_BaseRateLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_VariableRateAxis
= wtfc_HighestRateMember
                     
Base Rate Loan [Member] | Highest Rate [Member] | Term Facility [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 0.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_BaseRateLoanMember
/ us-gaap_LongtermDebtTypeAxis
= wtfc_TermFacilityMember
/ us-gaap_VariableRateAxis
= wtfc_HighestRateMember
                     
Base Rate Loan [Member] | Prime Rate [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 0.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_BaseRateLoanMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
                     
Base Rate Loan [Member] | Eurodollar [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_BaseRateLoanMember
/ us-gaap_VariableRateAxis
= us-gaap_EurodollarMember
                     
Eurodollar Rate Loan [Member] | Highest Rate [Member] | Revolving Credit Facility [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_EurodollarRateLoanMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_VariableRateAxis
= wtfc_HighestRateMember
                     
Eurodollar Rate Loan [Member] | Highest Rate [Member] | Term Facility [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 1.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_EurodollarRateLoanMember
/ us-gaap_LongtermDebtTypeAxis
= wtfc_TermFacilityMember
/ us-gaap_VariableRateAxis
= wtfc_HighestRateMember
                     
Eurodollar Rate Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]                        
Debt Instrument [Line Items]                        
Debt Instrument, Basis Spread on Variable Rate 0.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ wtfc_LoanTypeUnderBorrowingAgreementAxis
= wtfc_EurodollarRateLoanMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember