Capital Requirements (Details 2) (USD $) In Thousands, unless otherwise specified	0 Months Ended
Jan. 01, 2015	Dec. 31, 2014	Dec. 31, 2013
Capital Requirements
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%
Forecast
Capital Requirements
Total Capital (to Risk Weighted Assets), Actual Amount	$ 500,000
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)	4.50%
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)	2.50%
Term of mandatory compliance	4 years
Parent Company
Capital Requirements
Total Capital (to Risk Weighted Assets), Actual Amount		1,524,998	1,442,837
Tier 1 Capital (to Risk Weighted Assets), Actual Amount		1,457,068	1,369,657
Tier 1 Capital (to Average Assets), Actual Amount		1,457,068	1,369,657
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		20.24%	20.36%
Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		19.34%	19.33%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)		12.33%	11.61%
Parent Company \| Minimum
Capital Requirements
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		602,847	566,870
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		301,424	283,435
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount		472,864	472,044
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		8.00%	8.00%
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
International Bank of Commerce, Laredo
Capital Requirements
Total Capital (to Risk Weighted Assets), Actual Amount		1,131,528	1,035,189
Tier 1 Capital (to Risk Weighted Assets), Actual Amount		1,071,360	969,731
Tier 1 Capital (to Average Assets), Actual Amount		1,071,360	969,731
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		17.31%	16.96%
Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		16.39%	15.89%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)		11.22%	10.09%
International Bank of Commerce, Laredo \| Minimum
Capital Requirements
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		523,006	488,303
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		653,757	610,378
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		261,503	244,151
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		392,254	366,227
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount		381,804	384,497
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		477,255	480,622
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		8.00%	8.00%
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		6.00%	6.00%
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%
International Bank of Commerce, Brownsville
Capital Requirements
Total Capital (to Risk Weighted Assets), Actual Amount		151,489	143,879
Tier 1 Capital (to Risk Weighted Assets), Actual Amount		145,584	138,467
Tier 1 Capital (to Average Assets), Actual Amount		145,584	138,467
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		28.60%	27.63%
Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		27.48%	26.60%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)		13.96%	13.33%
International Bank of Commerce, Brownsville \| Minimum
Capital Requirements
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		42,381	41,652
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		52,976	52,065
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		21,190	20,826
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		31,785	31,239
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount		41,717	41,553
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		52,146	51,942
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		8.00%	8.00%
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		6.00%	6.00%
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%
International Bank of Commerce, Zapata
Capital Requirements
Total Capital (to Risk Weighted Assets), Actual Amount		60,946	57,675
Tier 1 Capital (to Risk Weighted Assets), Actual Amount		60,035	56,459
Tier 1 Capital (to Average Assets), Actual Amount		60,035	56,459
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		33.83%	32.65%
Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		33.33%	31.96%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)		10.88%	10.64%
International Bank of Commerce, Zapata \| Minimum
Capital Requirements
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		14,412	14,130
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		18,041	17,663
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		7,206	7,065
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		10,809	10,598
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount		22,081	21,219
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		27,602	26,523
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		8.00%	8.00%
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		6.00%	6.00%
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%
Commerce Bank
Capital Requirements
Total Capital (to Risk Weighted Assets), Actual Amount		68,291	64,585
Tier 1 Capital (to Risk Weighted Assets), Actual Amount		67,347	63,491
Tier 1 Capital (to Average Assets), Actual Amount		67,347	63,491
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		37.42%	36.45%
Tier 1 Capital (to Risk Weighted Assets), Actual Ratio (as a percent)		36.90%	35.83%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)		12.04%	11.88%
Commerce Bank \| Minimum
Capital Requirements
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		14,600	14,175
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		18,251	17,719
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Amount		7,300	7,087
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		10,950	10,631
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Amount		22,373	21,372
Tier 1 Capital (to Average Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount		27,966	$ 26,715
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		8.00%	8.00%
Total Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Risk Weighted Assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		6.00%	6.00%
Tier 1 Capital (to Average Assets), For Capital Adequacy Purposes Ratio (as a percent)		4.00%	4.00%
Tier 1 Capital (to Average Assets), To Be well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)		5.00%	5.00%

Period representing the new rule of mandatory compliance.

No definition available.

Name:	iboc_MandatoryComplianceTerm
Namespace Prefix:	iboc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of total capital as defined in the regulations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

+ Details

Name:	us-gaap_Capital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=iboc_CommerceBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=iboc_InternationalBankOfCommerceBrownsvilleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=iboc_InternationalBankOfCommerceLaredoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=iboc_InternationalBankOfCommerceZapataMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: