Loans (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Loans [Abstract]
Unearned income on premium finance receivables	$ 36.8	$ 34.6	$ 34.6
Deferred loan fees and costs net, including fair value purchase accounting adjustments	$ 12.6	$ 12.8	$ 11.5

Deferred loan fees and costs net including purchase accounting adjustments

No definition available.

Name:	wtfc_DeferredLoanFeesAndCostsNetIncludingPurchaseAccountingAdjustments
Namespace Prefix:	wtfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant