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Other Borrowed Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Other Borrowed Funds
Other borrowed funds	$ 941,457us-gaap_AdvancesFromFederalHomeLoanBanks	$ 1,073,944us-gaap_AdvancesFromFederalHomeLoanBanks
Percentage of decrease in other borrowed funds	12.30%iboc_PercentageOfAdvancesFromFederalHomeLoanBanksIncreaseDecrease

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- Definition

Represents the percentage change in other borrowed funds. Borrowed funds primarily consist of short and long term borrowings from the Federal Home Loan Bank.

+ References

No definition available.

+ Details

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- Definition

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

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