Derivative Instruments and Other Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Cash as collateral for derivative transactions	$ 2,650,000	$ 2,650,000
Fair value of derivatives	$ 563,000

Total fair value of derivatives at the end of the current period that are scheduled to mature within the next 12 months

No definition available.

Name:	ibkc_FairValueOfDerivatives
Namespace Prefix:	ibkc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant