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Bank Premises and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Bank premises and equipment
Less: accumulated depreciation	(378,682)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	$ (355,792)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
Bank premises and equipment, net	526,423us-gaap_PropertyPlantAndEquipmentNet	504,842us-gaap_PropertyPlantAndEquipmentNet
Bank buildings and improvements
Bank premises and equipment
Bank premises and equipment, gross	509,830us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_BuildingAndBuildingImprovementsMember	470,386us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_BuildingAndBuildingImprovementsMember
Bank buildings and improvements | Minimum
Bank premises and equipment
Estimated useful lives	5 years
Bank buildings and improvements | Maximum
Bank premises and equipment
Estimated useful lives	40 years
Furniture, equipment and vehicles
Bank premises and equipment
Bank premises and equipment, gross	269,861us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = iboc_FurnitureEquipmentAndVehiclesMember	260,932us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = iboc_FurnitureEquipmentAndVehiclesMember
Furniture, equipment and vehicles | Minimum
Bank premises and equipment
Estimated useful lives	1 year
Furniture, equipment and vehicles | Maximum
Bank premises and equipment
Estimated useful lives	20 years
Land
Bank premises and equipment
Bank premises and equipment, gross	125,414us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandMember	128,805us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_LandMember
Land, building, furniture, fixture and equipment
Bank premises and equipment
Bank premises and equipment, gross		$ 511us-gaap_PropertyPlantAndEquipmentGross / us-gaap_PropertyPlantAndEquipmentByTypeAxis = iboc_LandBuildingFurnitureFixtureAndEquipmentMember
Land, building, furniture, fixture and equipment | Minimum
Bank premises and equipment
Estimated useful lives	7 years
Land, building, furniture, fixture and equipment | Maximum
Bank premises and equipment
Estimated useful lives	27 years

X

- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.14)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 14

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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X

- Definition

Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 13

-Subparagraph a

-Article 5



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 8

-Article 7

+ Details

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X

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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- Details

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