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Loans Loans (Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period) (Details) (Delavan Bancshares, USD $)
In Thousands, unless otherwise specified
Jan. 16, 2015
Delavan Bancshares
  
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]  
Contractually required payments including interest $ 15,791us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DelavanBancsharesMember
Less: Nonaccretable difference 1,442us-gaap_CertainLoansAcquiredInTransferNonaccretableDifference
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DelavanBancsharesMember
Cash flows expected to be collected 14,349us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DelavanBancsharesMember		 [1]
Less: Accretable yield 898us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DelavanBancsharesMember
Fair value of PCI loans acquired $ 13,451us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DelavanBancsharesMember
[1] Represents undiscounted expected principal and interest cash at acquisition.