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Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2015 item
Basis of Presentation
Number of operating segments	1us-gaap_NumberOfOperatingSegments
Number of active operating bank subsidiaries	4iboc_NumberOfActiveOperatingSubsidiaries

X

- Details

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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.

+ References

No definition available.

+ Details

Name:	iboc_NumberOfActiveOperatingSubsidiaries
Namespace Prefix:	iboc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- 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