Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Consolidated
Tier 1 Leverage
Minimum amount	$ 754,230	$ 602,387
Minimum ratio	4.00%	4.00%
Actual amount	$ 1,758,666	$ 1,408,842
Actual ratio	9.33%	9.36%
Common Equity Tier 1 (CET1)
Minimum amount	$ 737,629
Minimum ratio	4.50%
Actual amount	$ 1,652,078
Actual ratio	10.08%
Tier 1 Risk-Based Capital
Minimum amount	$ 983,506	$ 504,114
Minimum ratio	6.00%	4.00%
Actual amount	$ 1,758,666	$ 1,408,842
Actual ratio	10.73%	11.18%
Total Risk-Based Capital
Minimum amount	$ 1,311,341	$ 1,008,227
Minimum ratio	8.00%	8.00%
Actual amount	$ 1,990,821	$ 1,550,789
Actual ratio	12.15%	12.31%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 751,378	$ 600,149
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 939,222	$ 750,186
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 1,647,804	$ 1,266,241
Actual ratio	8.77%	8.44%
Common Equity Tier 1 (CET1)
Minimum amount	$ 735,647
Minimum ratio	4.50%
Well capitalized amount	$ 1,062,601
Well capitalized ratio	6.50%
Actual amount	$ 1,647,804
Actual ratio	10.08%
Tier 1 Risk-Based Capital
Minimum amount	$ 980,863	$ 502,421
Minimum ratio	6.00%	4.00%
Well capitalized amount	$ 1,307,817	$ 753,631
Well capitalized ratio	8.00%	6.00%
Actual amount	$ 1,647,804	$ 1,266,241
Actual ratio	10.08%	10.08%
Total Risk-Based Capital
Minimum amount	$ 1,307,817	$ 1,004,841
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 1,634,772	$ 1,256,052
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 1,792,584	$ 1,408,188
Actual ratio	10.97%	11.21%