Goodwill and Other Acquired Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Goodwill And Other Intangibles [Line Items]
Impairment of goodwill	$ 9.7
Other Assets [Member]
Goodwill And Other Intangibles [Line Items]
Title plant assets	$ 6.7	$ 6.7

The cumulative amount of goodwill impairment losses recognized in the Company's statement of comprehensive income for periods prior to those presented.

No definition available.

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