Derivative Financial Instruments Derivative Financial Instruments (Schedule Of Cash Flow Hedging Instruments) (Detail) $ in Thousands	Sep. 30, 2015 USD ($)
Total Interest Rate Cap
Derivative [Line Items]
Notional amount	$ 796,500
Fair Value Asset (Liability)	300
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Swap Fifty Million Notional September Two Thousand Sixteen Maturity
Derivative [Line Items]
Notional amount	50,000
Fair Value Asset (Liability)	(862)
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Swap Twenty Five Million Notional October Two Thousand Sixteen Maturity
Derivative [Line Items]
Notional amount	25,000
Fair Value Asset (Liability)	(467)
Cash Flow Hedging \| Designated as Hedging Instrument \| Total Interest Rate Swap
Derivative [Line Items]
Notional amount	75,000
Fair Value Asset (Liability)	(1,329)
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Cap Forty Three Million Five Hundred Thousand Notional August Two Thousand Sixteen Maturity
Derivative [Line Items]
Notional amount	43,500
Fair Value Asset (Liability)	2
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Cap Two Hundred Sixteen Million Five Hundred Thousand Notional August Two Thousand Sixteen Maturity
Derivative [Line Items]
Notional amount	216,500
Fair Value Asset (Liability)	5
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Cap Fifty Million Notional September Two Thousand Seventeen Maturity
Derivative [Line Items]
Notional amount	50,000
Fair Value Asset (Liability)	112
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Cap Forty Million Notional September Two Thousand Seventeen Maturity
Derivative [Line Items]
Notional amount	40,000
Fair Value Asset (Liability)	97
Cash Flow Hedging \| Designated as Hedging Instrument \| Total Interest Rate Cap
Derivative [Line Items]
Notional amount	350,000
Fair Value Asset (Liability)	216
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Swaps and Caps
Derivative [Line Items]
Notional amount	425,000
Fair Value Asset (Liability)	$ (1,113)

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of interest rate derivative assets, net of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611

+ Details

Name:	us-gaap_InterestRateDerivativesAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_TotalInterestRateCapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateSwapFiftyMillionNotionalSeptemberTwoThousandSixteenMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateSwapTwentyFiveMillionNotionalOctoberTwoThousandSixteenMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_TotalInterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateCapFortyThreeMillionFiveHundredThousandNotionalAugustTwoThousandSixteenMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateCapTwoHundredSixteenMillionFiveHundredThousandNotionalAugustTwoThousandSixteenMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateCapFiftyMillionNotionalSeptemberTwoThousandSeventeenMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateCapFortyMillionNotionalSeptemberTwoThousandSeventeenMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wtfc_InterestRateDerivativesByTypeAxis=wtfc_InterestRateSwapsAndCapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: