XML 42 R118.htm IDEA: XBRL DOCUMENT v2.4.1.9
Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Derivative assets subject to master netting arrangements, Gross Amounts $ 28,798us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral $ 26,422us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
Derivative liabilities subject to master netting arrangements, Gross Amounts 15,411us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral 10,620us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
Derivative assets subject to master netting arrangements, Gross Amounts Not Offset 28,798us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral 26,422us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
Derivative liabilities subject to master netting arrangements, Gross Amounts Not Offset 11,676us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral 5,201us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
Collateral [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Derivative liabilities subject to master netting arrangements, Gross Amounts Not Offset (3,735)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_FinancialInstrumentAxis
= ibkc_CollateralMember		 (5,419)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_FinancialInstrumentAxis
= ibkc_CollateralMember
Interest Rate Contracts [Member] | Not Designated as Hedging Instruments [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Derivative assets subject to master netting arrangements, Gross Amounts 15,411us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 10,621us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Derivative liabilities subject to master netting arrangements, Gross Amounts 15,411us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 10,620us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Derivative assets subject to master netting arrangements, Gross Amounts Not Offset 15,411us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 10,621us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Derivative liabilities subject to master netting arrangements, Gross Amounts Not Offset 11,676us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 5,201us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Interest Rate Contracts [Member] | Collateral [Member] | Not Designated as Hedging Instruments [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Derivative liabilities subject to master netting arrangements, Gross Amounts Not Offset (3,735)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_CollateralMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 (5,419)us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_CollateralMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Written and Purchased Options [Member]    
Derivative Instruments and Hedging Activities Disclosures [Line Items]    
Derivative assets subject to master netting arrangements, Gross Amounts 13,387us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= ibkc_WrittenAndPurchaseOptionsMember		 15,801us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= ibkc_WrittenAndPurchaseOptionsMember
Derivative assets subject to master netting arrangements, Gross Amounts Not Offset $ 13,387us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= ibkc_WrittenAndPurchaseOptionsMember		 $ 15,801us-gaap_DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral
/ us-gaap_DerivativeInstrumentRiskAxis
= ibkc_WrittenAndPurchaseOptionsMember