Disposition Activity - Schedule of Branch Closure Costs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Business Combinations [Abstract]
Employee termination	$ 55
Accelerated depreciation	375
Total	$ 430

Business Disposition Cost Of Disposed Entity Transaction Costs

No definition available.

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