Name:	iboc_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecreaseLoansTransferredToOtherRealEstateOwned
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Reflects the amount of charge-off related to a loan prior to foreclosure.

No definition available.

Name:	iboc_AllowanceForLoanLeaseLossesWriteOffsPriorToForeclosure
Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The estimated fair value of recorded investment related to change in provision for impaired financing receivables measured at fair value.

No definition available.

Name:	iboc_ChangeInProvisionOfImpairedFinancingReceivableFairValueDisclosure
Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying amount as of the balance sheet date of change in Provision of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

No definition available.

Name:	iboc_ChangeInProvisionOfOtherRealEstateAndForeclosedAssetsInUse
Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The decline in the loss severity rate assumptions for the following five years used in the discounted cash flow model for investments classified within level 3 of the fair value hierarchy.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelAssumptionsDeclineInLossSeverityRatesForFollowingFifthYear
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
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Default rate assumption used in the discounted cash flow model for investments classified within level 3 of the fair value hierarchy.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelAssumptionsDefaultRates
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The discount rate assumption of estimated future principal prepayment rate assumption used in the discounted cash flow model for investments classified within level 3 of the fair value hierarchy.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelAssumptionsFuturePrincipalPrepaymentDiscountRate
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The low end of range of estimated future principal prepayment rate assumption used in the discounted cash flow model for investments classified within level 3 of the fair value hierarchy.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelAssumptionsFuturePrincipalPrepaymentRatesLowEndOfRange
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Loss severity rates assumption for the first year used in the discounted cash flow model for investments classified within level 3 of the fair value hierarchy.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelAssumptionsLossSeverityRatesForFirstYear
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Loss severity rates assumption for the remaining years used in the discounted cash flow model for investments classified within level 3 of the fair value hierarchy.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelAssumptionsLossSeverityRatesThereafter
Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The minimum period where the underlying residential mortgage loans must perform under original contract terms as a basis for certain discounted cash flow assumptions to be used.

No definition available.

Name:	iboc_FairValueMeasurementsDiscountedCashFlowModelMinimumPerformancePeriodUnderOriginalTerms
Namespace Prefix:	iboc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The impaired collateral dependent commercial loans where an internal evaluation has been done in the last twelve months.

No definition available.

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

Represents the impaired commercial collateral dependent financing receivables where the basis for fair value is an appraisal obtained in the last twelve months.

No definition available.

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

The estimated fair value of the recorded impaired collateral measured on a non-recurring basis as of the reporting date.

No definition available.

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

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

No definition available.

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

- References

No definition available.

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

- References

No definition available.

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

- References

No definition available.

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

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=iboc_BondMeetingOriginalContractTermsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=iboc_BondNotMeetingOriginalContractTermsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
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Period Type: