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Consolidated Statements of Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Consolidated Statements of Income
Impairment charges, other-than-temporary impairment charges	$ 122iboc_OtherThanTemporaryImpairmentLossesInvestmentPortionRecognizedInEarningsNet	$ 32iboc_OtherThanTemporaryImpairmentLossesInvestmentPortionRecognizedInEarningsNet
Impairment charges, other comprehensive (loss) income	$ (349)us-gaap_OtherComprehensiveIncomeLossBeforeTax	$ (122)us-gaap_OtherComprehensiveIncomeLossBeforeTax

X

- Definition

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of the amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

+ References

No definition available.

+ Details

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Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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- Details

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

X

- Definition

Amount before tax, after reclassification adjustments of other comprehensive income (loss).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669619-108580



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669625-108580



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33775-111570

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	duration