Represents the estimated fair value of letters of credit outstanding at the balance sheet date.

No definition available.

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

- References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

+ Details

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- Definition

The amount of loss pertaining to the specified contingency that was charged against earnings in the period, including the effects of revisions in previously reported estimates.

+ References

+ Details

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- Details

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Commitments and Contingencies (Detail) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Dec. 11, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Fair value of guarantees under commercial and standby letters of credit				$ 2.1	$ 1.6
Loss Contingencies [Line Items]
Loss recognized				$ 11.7
Settled Litigation
Loss Contingencies [Line Items]
Loss recognized	$ 11.7
Pending Litigation
Loss Contingencies [Line Items]
Accrual for potential loss		$ 5.7	$ 6.0