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Capital Requirements and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Consolidated [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Tier 1 Leverage, Minimum Amount $ 602,387us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 $ 507,760us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 risk-based capital, Minimum Amount 504,114us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 426,002us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Total risk-based capital, Minimum Amount 1,008,227us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 852,005us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 Leverage capital, Minimum Ratio 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 risk-based capital, Minimum Ratio 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Total risk-based capital, Minimum Ratio 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 Leverage, Actual Amount 1,408,842us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 1,231,886us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 risk-based capital, Actual Amount 1,408,842us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 1,231,886us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Total risk-based capital, Actual Amount 1,550,789us-gaap_Capital
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 1,365,280us-gaap_Capital
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 Leverage, Actual Ratio 9.36%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 9.70%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Tier 1 risk-based capital, Actual Ratio 11.18%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 11.57%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
Total risk-based capital, Actual Ratio 12.31%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember		 12.82%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= ibkc_ConsolidatedMember
IBERIABANK [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Tier 1 Leverage, Minimum Amount 600,149us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 505,723us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 risk-based capital, Minimum Amount 502,421us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 424,578us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Total risk-based capital, Minimum Amount 1,004,841us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 849,157us-gaap_CapitalRequiredForCapitalAdequacy
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 Leverage capital, Minimum Ratio 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 risk-based capital, Minimum Ratio 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Total risk-based capital, Minimum Ratio 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 Leverage capital, Well Capitalized Amount 750,186us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 632,154us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 risk-based capital, Well Capitalized Amount 753,631us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 636,868us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Total risk-based capital, Well Capitalized Amount 1,256,052us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 1,061,446us-gaap_CapitalRequiredToBeWellCapitalized
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 Leverage capital, Well Capitalized Ratio 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 risk-based capital, Well Capitalized Ratio 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Total risk-based capital, Well Capitalized Ratio 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 Leverage, Actual Amount 1,266,241us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 1,069,783us-gaap_TierOneLeverageCapital
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 risk-based capital, Actual Amount 1,266,241us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 1,069,783us-gaap_TierOneRiskBasedCapital
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Total risk-based capital, Actual Amount $ 1,408,188us-gaap_Capital
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 $ 1,202,738us-gaap_Capital
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 Leverage, Actual Ratio 8.44%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 8.46%us-gaap_TierOneLeverageCapitalToAverageAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Tier 1 risk-based capital, Actual Ratio 10.08%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 10.08%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
Total risk-based capital, Actual Ratio 11.21%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		 11.33%us-gaap_CapitalToRiskWeightedAssets
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember