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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

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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.

+ 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