The amount of loans approved and closed as part of the lending program.

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

The term of financing receivables.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
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- Definition

Amount of financing receivable with some degree of payment deferrals.

+ References

No definition available.

+ Details

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Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The contractual interest rate on financing receivable.

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
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- Definition

Represents the period of time the PPP loans are intended to support payroll and certain other costs to help businesses remain viable and allow their employees to pay their bills.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
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- Definition

The number of loans approved and closed as part of the lending program.

+ References

No definition available.

+ Details

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Namespace Prefix:	iboc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

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

- Definition

Threshold period for when financing receivable is considered past due to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-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

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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Namespace Prefix:
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- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=iboc_PaycheckProtectionProgramLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	srt_StatementScenarioAxis=iboc_LoanScenarioOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	srt_StatementScenarioAxis=iboc_LoanScenarioTwoMember
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Data Type:	na
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- Details

Name:	us-gaap_GeographicDistributionAxis=us-gaap_GeographicDistributionDomesticMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LienCategoryAxis=us-gaap_SeniorLienMember
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Data Type:	na
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- Details

Name:	us-gaap_LienCategoryAxis=us-gaap_JuniorLienMember
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- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
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Allowance for Credit Losses (Impaired Loans) (Details)	12 Months Ended
Allowance for Credit Losses (Impaired Loans) (Details)	Dec. 31, 2021 USD ($)	Feb. 18, 2022 USD ($) loan	Dec. 31, 2020 USD ($)
Interest Recognized
Total troubled debt restructuring	$ 3,253,000		$ 5,821,000
Period of charge off for past due unsecured commercial loans	90 days
Subsequent Event
Interest Recognized
Amount of loans with some degree of payment deferral		$ 123,194,000
Paycheck protection program loans (COVID-19 program)
Interest Recognized
Period of time PPP loans cover payroll and certain other costs	168 days
Interest rate on receivable	1.00%
Paycheck protection program loans (COVID-19 program) \| Subsequent Event
Interest Recognized
Number of loans \| loan		968
Amount of loans outstanding		$ 71,149,000
Paycheck protection program loans (COVID-19 program) \| Loans made prior to June 5, 2020
Interest Recognized
Term of receivable (in years)	2 years
Paycheck protection program loans (COVID-19 program) \| Loans made after June 5, 2020
Interest Recognized
Term of receivable (in years)	5 years
Domestic \| Residential: first lien
Interest Recognized
Total troubled debt restructuring	$ 2,254,000		4,078,000
Domestic \| Residential Junior Lien
Interest Recognized
Total troubled debt restructuring	105,000		521,000
Consumer \| Domestic
Interest Recognized
Total troubled debt restructuring	878,000		989,000
Foreign. \| Foreign
Interest Recognized
Total troubled debt restructuring	$ 16,000		$ 233,000