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Loans (Schedule of Unpaid Principal Balance And Carrying Value Of Acquired Loans) (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Bank acquisitions    
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]    
Unpaid Principal Balance $ 277,163us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember		 $ 285,809us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember
Carrying Value 222,837us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember		 227,229us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_BankAcquisitionsMember
Life insurance premium finance loans acquisition    
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]    
Unpaid Principal Balance 394,632us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember		 399,665us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember
Carrying Value $ 389,048us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember		 $ 393,479us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet
/ us-gaap_BusinessAcquisitionAxis
= wtfc_LifeInsurancePremiumFinanceAcquisitionMember