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Loans and mortgage loans held for sale.

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No definition available.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Carrying amount of receivable assets originating from the indemnification agreement with the Federal Deposit Insurance Corporation (FDIC), in which the FDIC is to partially cover losses.

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

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Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financial Assets
Cash and cash equivalents	$ 967,290	$ 548,095	$ 430,308	$ 391,396
Loans and loans held for sale, net of unearned income	13,088,505ibkc_LoansAndLoansMortgageHeldForSale		9,772,772ibkc_LoansAndLoansMortgageHeldForSale
FDIC loss share receivable	60,972us-gaap_FDICIndemnificationAsset	69,627us-gaap_FDICIndemnificationAsset
Financial Liabilities
Deposits	14,668,073us-gaap_Deposits	12,520,525us-gaap_Deposits	10,898,863us-gaap_Deposits
Short-term borrowings	604,902us-gaap_ShortTermBorrowings	845,742us-gaap_ShortTermBorrowings
Long-term debt	460,889us-gaap_LongTermDebt	403,254us-gaap_LongTermDebt
Carrying Amount [Member]
Financial Assets
Cash and cash equivalents	967,290	548,095
Investment securities	2,456,055	2,275,813
Loans and loans held for sale, net of unearned income	13,088,505	11,581,116
FDIC loss share receivable	60,972	69,627
Derivative instruments	41,120	32,903
Accrued interest receivable	41,865	37,696
Financial Liabilities
Deposits	14,668,073	12,520,525
Short-term borrowings	604,902	845,742
Long-term debt	460,889	403,254
Derivative instruments	35,704	31,354
Accrued interest payable	9,281	8,258
Fair Value [Member]
Financial Assets
Cash and cash equivalents	967,290	548,095
Investment securities	2,458,984	2,278,334
Loans and loans held for sale, net of unearned income	13,070,985	11,605,446
FDIC loss share receivable	39,540	19,606
Derivative instruments	41,120	32,903
Accrued interest receivable	41,865	37,696
Financial Liabilities
Deposits	14,489,153	12,298,017
Short-term borrowings	604,902	845,742
Long-term debt	440,158	376,139
Derivative instruments	35,704	31,354
Accrued interest payable	9,281	8,258
Level 1 [Member]
Financial Assets
Cash and cash equivalents	967,290	548,095
Investment securities	67,206
Accrued interest receivable	41,865	37,696
Financial Liabilities
Short-term borrowings	604,902	845,742
Accrued interest payable	9,281	8,258
Level 2 [Member]
Financial Assets
Investment securities	2,391,778	2,278,334
Loans and loans held for sale, net of unearned income	194,816	139,950
Derivative instruments	41,120	32,903
Financial Liabilities
Derivative instruments	35,704	31,354
Level 3 [Member]
Financial Assets
Loans and loans held for sale, net of unearned income	12,876,169	11,465,496
FDIC loss share receivable	39,540	19,606
Financial Liabilities
Deposits	14,489,153	12,298,017
Long-term debt	$ 440,158	$ 376,139