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Loans (Unpaid Principal Balance and Carrying Value of Acquired Loans) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Bank acquisitions    
Loans [Line Items]    
Unpaid Principal Balance $ 285,809us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember		 $ 453,944us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember
Carrying Value 227,229us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember		 338,517us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember
Life insurance premium finance loans acquisition    
Loans [Line Items]    
Unpaid Principal Balance 399,665us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember		 437,155us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember
Carrying Value $ 393,479us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember		 $ 423,906us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember