Allowance For Loan Losses And Credit Quality (Narrative) (Detail) (USD $)	Jun. 30, 2012
Allowance for loan losses on the non-covered loan portfolio	$ 3,828,000

Loans And Leases Receivables Allowance For Loan Losses

No definition available.

Name:	ibkc_LoansAndLeasesReceivablesAllowanceForLoanLosses
Namespace Prefix:	ibkc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant