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Federal Home Loan Bank Advances (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2014
Federal Home Loan Bank, Advances [Line Items]    
Federal Home Loan Bank advances, Restructured advances $ 292.5wtfc_FederalHomeLoanBankAdvancesRestructuredAdvances  
Federal Home Loan Bank advances, Prepayment fees 22.4us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresRepaymentAndPenalties  
Federal Home Loan Bank advances having varying put dates   35.0wtfc_FederalHomeLoanBankAdvancesHavingVaryingPutDates
Federal Home Loan Bank Advances [Member]    
Federal Home Loan Bank, Advances [Line Items]    
Weighted average interest rate   0.68%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresWeightedAverageInterestRate
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FederalHomeLoanBankAdvancesMember
Federal Home Loan Bank advances, Additional borrowings possible   $ 596.9us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FederalHomeLoanBankAdvancesMember