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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Period Type:	instant

- Definition

Represents the percentage of discount from redemption price of debt.

+ References

No definition available.

+ Details

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- 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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- 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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- 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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- Definition

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

+ References

No definition available.

+ Details

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- 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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- 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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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

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Details

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- Details

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Data Type:	na
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Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iboc_TrustTenAndElevenMember
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Data Type:	na
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- Details

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Junior Subordinated Interest Deferrable Debentures (Details)				9 Months Ended
	Jul. 29, 2015 USD ($)	Dec. 24, 2014 USD ($)	Feb. 11, 2014 USD ($)	Sep. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($)	Dec. 23, 2014 USD ($)
Junior subordinated deferrable interest debentures, major types of business trusts
Number of statutory business trusts issuing trust preferred securities \| item				7
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 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 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			26,990,000		$ 32,900,000
Trust X and XI
Junior subordinated deferrable interest debentures, major types of business trusts
Redemption price discount (as a percent)	24.50%
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