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Basis of Presentation (Details) | 6 Months Ended
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Jun. 30, 2015 item
Basis of Presentation |
Number of operating segments | 1
Number of active operating bank subsidiaries | 4

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- References No definition available. + Details
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Namespace Prefix: | iboc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the number of active operating subsidiaries of the entity. + References No definition available. + Details
Name: | iboc_NumberOfActiveOperatingSubsidiaries
Namespace Prefix: | iboc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
Name: | us-gaap_NumberOfOperatingSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration