Basis of Presentation (Details)	6 Months Ended
Jun. 30, 2012 entity segment
Basis of Presentation
Number of operating segments	1
Number of active operating bank subsidiaries	4

Represents the number of active operating subsidiaries of the entity.

No definition available.

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