XML 118 R98.htm IDEA: XBRL DOCUMENT v2.4.1.9
Allowance for Credit Losses and Credit Quality - Schedule of Investment in Impaired Loan (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Financing Receivable, Impaired [Line Items]    
Recorded Investment $ 36,560us-gaap_ImpairedFinancingReceivableRecordedInvestment $ 45,342us-gaap_ImpairedFinancingReceivableRecordedInvestment
Unpaid Principal Balance 37,327us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance 46,501us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Related Allowance (767)us-gaap_ImpairedFinancingReceivableRelatedAllowance (1,159)us-gaap_ImpairedFinancingReceivableRelatedAllowance
Average Recorded Investment 39,176us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment 49,645us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Interest Income Recognized 513us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod 587us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Commercial Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 11,443us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember		 25,018us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
Unpaid Principal Balance 11,876us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember		 25,877us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
Related Allowance (433)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember		 (859)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
Average Recorded Investment 12,851us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember		 28,823us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
Interest Income Recognized 251us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember		 321us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
Commercial Loans [Member] | With No Related Allowance Recorded [Member] | Real Estate [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 6,680us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 8,567us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Unpaid Principal Balance 6,680us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 8,567us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Average Recorded Investment 6,703us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 10,443us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Interest Income Recognized 132us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 43us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial Loans [Member] | With No Related Allowance Recorded [Member] | Business [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 2,483us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 13,256us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Unpaid Principal Balance 2,483us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 13,256us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Average Recorded Investment 2,873us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 11,074us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Interest Income Recognized 57us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 170us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Commercial Loans [Member] | With No Related Allowance Recorded [Member] | Home Equity [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 682us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 258us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Unpaid Principal Balance 682us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 258us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Average Recorded Investment 696us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 281us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Interest Income Recognized 19us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 1us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithNoRelatedAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Commercial Loans [Member] | With An Allowance Recorded [Member] | Real Estate [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 1,068us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 1,268us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Unpaid Principal Balance 1,093us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 1,284us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Related Allowance (25)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 (16)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Average Recorded Investment 1,158us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 4,414us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Interest Income Recognized 39us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 8us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial Loans [Member] | With An Allowance Recorded [Member] | Business [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 1,212us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 1,927us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Unpaid Principal Balance 1,620us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 2,770us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Related Allowance (408)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 (843)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Average Recorded Investment 2,117us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 2,892us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Interest Income Recognized 23us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember		 100us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= ibkc_BusinessMember
Mortgage Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 14,111us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember		 11,408us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
Unpaid Principal Balance 14,363us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember		 11,645us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
Related Allowance (252)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember		 (237)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
Average Recorded Investment 14,263us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember		 9,675us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
Interest Income Recognized 110us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember		 98us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
Mortgage Loans [Member] | With An Allowance Recorded [Member] | Residential Prime [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 10,532us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember		 9,791us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
Unpaid Principal Balance 10,768us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember		 10,019us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
Related Allowance (236)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember		 (228)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
Average Recorded Investment 10,577us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember		 8,096us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
Interest Income Recognized 11us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember		 98us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPrimeFinancingReceivableMember
Mortgage Loans [Member] | With An Allowance Recorded [Member] | Residential Subprime [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 3,579us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember		 1,617us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember
Unpaid Principal Balance 3,595us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember		 1,626us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember
Related Allowance (16)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember		 (9)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember
Average Recorded Investment 3,686us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember		 1,579us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember
Interest Income Recognized 99us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= ibkc_MortgageLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialSubprimeFinancingReceivableMember		  
Consumer Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 11,006us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember		 8,916us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
Unpaid Principal Balance 11,088us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember		 8,979us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
Related Allowance (82)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember		 (63)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
Average Recorded Investment 12,062us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember		 11,147us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
Interest Income Recognized 152us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember		 168us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
Consumer Loans [Member] | With An Allowance Recorded [Member] | Home Equity [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 7,121us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 6,506us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Unpaid Principal Balance 7,165us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 6,550us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Related Allowance (44)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 (44)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Average Recorded Investment 7,544us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 7,593us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Interest Income Recognized 43us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember		 93us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Consumer Loans [Member] | With An Allowance Recorded [Member] | Indirect Automobile [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 1,410us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember		 1,267us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember
Unpaid Principal Balance 1,419us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember		 1,275us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember
Related Allowance (9)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember		 (8)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember
Average Recorded Investment 2,016us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember		 2,090us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember
Interest Income Recognized 51us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember		 55us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoansAutoFinancingReceivableMember
Consumer Loans [Member] | With An Allowance Recorded [Member] | Credit Card [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 1,012us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember		 404us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember
Unpaid Principal Balance 1,032us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember		 411us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember
Related Allowance (20)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember		 (7)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember
Average Recorded Investment 797us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember		 418us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember
Consumer Loans [Member] | With An Allowance Recorded [Member] | Consumer - Other [Member]    
Financing Receivable, Impaired [Line Items]    
Recorded Investment 781us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember		 481us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Unpaid Principal Balance 790us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember		 485us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Related Allowance (9)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember		 (4)us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Average Recorded Investment 1,009us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember		 765us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Interest Income Recognized $ 39us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember		 $ 19us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ibkc_WithAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ConsumerLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember