Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity).

Name:	us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DebtSecuritiesHeldToMaturityCreditQualityIndicatorLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount excluding accrued interest, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ References

+ Details

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

- Definition

Amount excluding accrued interest of investment in debt security measured at amortized cost (held-to-maturity) originated more than five years prior to current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

+ Details

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

- Definition

Amount excluding accrued interest of investment in debt security measured at amortized cost (held-to-maturity) originated four years prior to current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447

+ Details

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

- Definition

Amount excluding accrued interest of investment in debt security measured at amortized cost (held-to-maturity) originated three years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount excluding accrued interest of investment in debt security measured at amortized cost (held-to-maturity) originated in current fiscal year.

+ References

+ Details

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

- Definition

Amount excluding accrued interest of investment in debt security measured at amortized cost (held-to-maturity) originated two years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount excluding accrued interest of investment in debt security measured at amortized cost (held-to-maturity) originated in fiscal year prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27232-111563

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=wtfc_InternalInvestmentGrade1To4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=wtfc_InternalInvestmentGrade5To7Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=wtfc_InternalInvestmentGrade8To10Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateNoteSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Allowance for Credit Losses (Held-to-Maturity Debt Securities by Credit Quality Indication) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	$ 3,435,888	$ 2,942,363	$ 2,166,518
Less: Allowance for credit losses	(159)	(78)	(99)
Held-to-maturity securities, net of allowance for credit losses	3,435,729	2,942,285	2,166,419
U.S. Government agencies
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	85,000
2021	147,795
2020	25,000
2019	4,032
2018	0
Prior	2,834
Amortized Cost	264,661	180,192	176,160
U.S. Government agencies \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	85,000
2021	147,795
2020	25,000
2019	4,032
2018	0
Prior	2,834
Amortized Cost	264,661
U.S. Government agencies \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
U.S. Government agencies \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
Municipal
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	7,067
2020	300
2019	160
2018	7,465
Prior	165,556
Amortized Cost	180,548	$ 187,486	$ 197,865
Municipal \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	7,067
2020	300
2019	160
2018	7,465
Prior	165,556
Amortized Cost	180,548
Municipal \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
Municipal \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
Mortgage-backed securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	379,444
2021	2,567,451
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	2,946,895
Mortgage-backed securities \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	379,444
2021	2,567,451
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	2,946,895
Mortgage-backed securities \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
Mortgage-backed securities \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
Corporate notes
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	6,012
2019	7,377
2018	3,244
Prior	27,151
Amortized Cost	43,784
Corporate notes \| 1-4 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	6,012
2019	7,377
2018	3,244
Prior	27,151
Amortized Cost	43,784
Corporate notes \| 5-7 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	0
Corporate notes \| 8-10 internal grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	0
Amortized Cost	$ 0