Represents capital securities issued by trust that is qualified as Tier I capital as on the reporting date.

No definition available.

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Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the percentage of discount from redemption price of debt.

+ References

No definition available.

+ Details

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Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the maximum number of consecutive quarterly periods available to the entity for deferring the payment of interest on Trusts VI, VII, VIII, IX, X, XI and XII.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the maximum percentage of capital securities issued by the trust qualifying as Tier I capital on an aggregate basis.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum percentage of capital securities issued by the trust qualifying as Tier II capital on an aggregate basis.

+ References

No definition available.

+ Details

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Namespace Prefix:	iboc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of statutory business trusts formed for the purpose of issuing trust preferred securities.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

Name:	us-gaap_RepaymentsOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustSixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustSevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustTenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustTenAndElevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustElevenMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustTwelveMember
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Junior Subordinated Deferrable Interest Debentures (Details)				12 Months Ended
	Jul. 29, 2015 USD ($)	Dec. 24, 2014 USD ($)	Feb. 11, 2014 USD ($)	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($)
Junior subordinated deferrable interest debentures, major types of business trusts
Number of statutory business trusts issuing trust preferred securities \| item				6
Junior subordinated deferrable interest debentures				$ 161,416,000	$ 175,416,000
Maximum number of consecutive quarterly period available for deferral of interest payment on Trusts VI, VII, VIII, IX, X, XI and XII \| item				20
Percentage of capital securities issued by trust qualifying as Tier I capital, maximum				25.00%
Percentage of capital securities issued by trust qualifying as Tier II capital, minimum				25.00%
Capital securities issued by the trust, qualifying as Tier I capital				$ 161,416,000	$ 175,416,000
Trust VI
Junior subordinated deferrable interest debentures, major types of business trusts
Junior subordinated deferrable interest debentures				25,774,000
Trust VII
Junior subordinated deferrable interest debentures, major types of business trusts
Redemption price discount (as a percent)			6.00%
Retirement of capital securities			$ 10,310,000
Trust VIII
Junior subordinated deferrable interest debentures, major types of business trusts
Junior subordinated deferrable interest debentures				25,774,000
Trust IX
Junior subordinated deferrable interest debentures, major types of business trusts
Junior subordinated deferrable interest debentures				41,238,000
Trust X
Junior subordinated deferrable interest debentures, major types of business trusts
Retirement of capital securities	$ 13,000,000
Junior subordinated deferrable interest debentures	34,021,000			$ 21,021,000
Trust X and XI
Junior subordinated deferrable interest debentures, major types of business trusts
Redemption price discount (as a percent)				24.50%
Trust XI
Junior subordinated deferrable interest debentures, major types of business trusts
Redemption price discount (as a percent)		23.60%
Retirement of capital securities	1,000,000	$ 5,000,000
Junior subordinated deferrable interest debentures	$ 27,900,000	$ 32,900,000		$ 26,990,000
Trust XII
Junior subordinated deferrable interest debentures, major types of business trusts
Junior subordinated deferrable interest debentures				$ 20,619,000