Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Consolidated
Tier 1 Leverage
Minimum amount	$ 845,887	$ 818,440
Minimum ratio	4.00%	4.00%
Actual amount	$ 2,730,832	$ 2,221,528
Actual ratio	12.91%	10.86%
Common Equity Tier 1 (CET1)
Minimum amount	$ 798,791	$ 794,334
Minimum ratio	4.50%	4.50%
Actual amount	$ 2,598,735	$ 2,089,431
Actual ratio	14.64%	11.84%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,065,054	$ 1,059,112
Minimum ratio	6.00%	6.00%
Actual amount	$ 2,730,832	$ 2,221,528
Actual ratio	15.38%	12.59%
Total Risk-Based Capital (1)
Minimum amount	$ 1,420,073	$ 1,412,149
Minimum ratio	8.00%	8.00%
Actual amount	$ 3,003,882	$ 2,493,988
Actual ratio	16.92%	14.13%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 843,399	$ 816,152
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 1,054,249	$ 1,020,190
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 1,925,529	$ 1,878,703
Actual ratio	9.13%	9.21%
Common Equity Tier 1 (CET1)
Minimum amount	$ 796,259	$ 792,111
Minimum ratio	4.50%	4.50%
Well capitalized amount	$ 1,150,153	$ 1,144,160
Well capitalized ratio	6.50%	6.50%
Actual amount	$ 1,925,529	$ 1,878,703
Actual ratio	10.88%	10.67%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,061,679	$ 1,056,147
Minimum ratio	6.00%	6.00%
Well capitalized amount	$ 1,415,572	$ 1,408,197
Well capitalized ratio	8.00%	8.00%
Actual amount	$ 1,925,529	$ 1,878,703
Actual ratio	10.88%	10.67%
Total Risk-Based Capital (1)
Minimum amount	$ 1,415,572	$ 1,408,197
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 1,769,465	$ 1,760,246
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 2,082,079	$ 2,034,663
Actual ratio	11.77%	11.56%