Loans - Schedule of Non-Covered and Covered Loans (Parenthetical) (Detail) (Covered Loans [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loan lost share coverage	$ 174.7

Represents the balance of loans as of the balance sheet date that will lose loss share coverage as of January 1, 2015.

No definition available.

Name:	ibkc_LoansAndLeasesReceivableGrossCarryingAmountCoveredLosingLossShareCoverage
Namespace Prefix:	ibkc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration