Commitments And Contingencies (Narrative) (Detail) (USD $)	Jun. 30, 2012
Fair value of guarantees under commercial and standby letters of credit	$ 429,000

Fair value of lines of credit at the balance sheet date.

No definition available.

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