Loans (Summary of Loan Portfolio) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 14,953,059	$ 14,409,398	$ 13,133,160
Covered loans	209,694	226,709	312,478
Total loans	15,162,753	14,636,107	13,445,638
Total loans, net of unearned income, excluding covered loans, percentage	99.00%	98.00%	98.00%
Covered loans, percentage	1.00%wtfc_PercentageOfCoveredLoans	2.00%wtfc_PercentageOfCoveredLoans	2.00%wtfc_PercentageOfCoveredLoans
Total loans, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	4,211,932	3,924,394	3,439,197
Total loans, net of unearned income, excluding covered loans, percentage	28.00%	26.00%	26.00%
Commercial real-estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	4,710,486	4,505,753	4,262,255
Total loans, net of unearned income, excluding covered loans, percentage	31.00%	31.00%	32.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	709,283	716,293	707,748
Total loans, net of unearned income, excluding covered loans, percentage	5.00%	5.00%	5.00%
Residential real-estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	495,925	483,542	426,769
Total loans, net of unearned income, excluding covered loans, percentage	3.00%	3.00%	3.00%
Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	2,319,623	2,350,833	2,208,361
Consumer and other
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	130,156	151,012	159,496
Total loans, net of unearned income, excluding covered loans, percentage	1.00%	1.00%	1.00%
Commercial insurance loans \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	2,319,623	2,350,833	2,208,361
Total loans, net of unearned income, excluding covered loans, percentage	15.00%	16.00%	17.00%
Life insurance \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 2,375,654	$ 2,277,571	$ 1,929,334
Total loans, net of unearned income, excluding covered loans, percentage	16.00%	16.00%	14.00%

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5074-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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