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Basis of Presentation (Details) | 9 Months Ended
--- | ---
Sep. 30, 2011 year segment entity day trust semiannual quarter
Basis of Presentation |
Number of operating segments | 1
Number of active operating bank subsidiaries | 4

X
- Details
Name: | iboc_BasisOfPresentationDisclosureAbstract
Namespace Prefix: | iboc
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of active operating subsidiaries of the entity. + Details
Name: | iboc_NumberOfActiveOperatingSubsidiaries
Namespace Prefix: | iboc
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of operating segments of the entity. + Details
Name: | iboc_OperatingSegmentNumber
Namespace Prefix: | iboc
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration