Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Consolidated
Tier 1 Leverage
Minimum amount	$ 845,167	$ 818,440
Minimum ratio	4.00%	4.00%
Actual amount	$ 2,787,729	$ 2,221,528
Actual ratio	13.19%	10.86%
Common Equity Tier 1 (CET1)
Minimum amount	$ 822,980	$ 794,334
Minimum ratio	4.50%	4.50%
Actual amount	$ 2,655,632	$ 2,089,431
Actual ratio	14.52%	11.84%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,097,306	$ 1,059,112
Minimum ratio	6.00%	6.00%
Actual amount	$ 2,787,729	$ 2,221,528
Actual ratio	15.24%	12.59%
Total Risk-Based Capital (1)
Minimum amount	$ 1,463,075	$ 1,412,149
Minimum ratio	8.00%	8.00%
Actual amount	$ 3,060,916	$ 2,493,988
Actual ratio	16.74%	14.13%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 842,313	$ 816,152
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 1,052,892	$ 1,020,190
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 1,994,073	$ 1,878,703
Actual ratio	9.47%	9.21%
Common Equity Tier 1 (CET1)
Minimum amount	$ 820,978	$ 792,111
Minimum ratio	4.50%	4.50%
Well capitalized amount	$ 1,185,857	$ 1,144,160
Well capitalized ratio	6.50%	6.50%
Actual amount	$ 1,994,073	$ 1,878,703
Actual ratio	10.93%	10.67%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,094,637	$ 1,056,147
Minimum ratio	6.00%	6.00%
Well capitalized amount	$ 1,459,516	$ 1,408,197
Well capitalized ratio	8.00%	8.00%
Actual amount	$ 1,994,073	$ 1,878,703
Actual ratio	10.93%	10.67%
Total Risk-Based Capital (1)
Minimum amount	$ 1,459,516	$ 1,408,197
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 1,824,395	$ 1,760,246
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 2,150,760	$ 2,034,663
Actual ratio	11.79%	11.56%