Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Consolidated
Tier 1 Leverage
Minimum amount	$ 768,953	$ 751,798
Minimum ratio	4.00%	4.00%
Actual amount	$ 1,864,891	$ 1,790,034
Actual ratio	9.70%	9.52%
Common Equity Tier 1 (CET1)
Minimum amount	$ 773,983	$ 752,610
Minimum ratio	4.50%	4.50%
Actual amount	$ 1,732,793	$ 1,684,097
Actual ratio	10.07%	10.07%
Tier 1 Risk-Based Capital
Minimum amount	$ 1,031,977	$ 1,003,479
Minimum ratio	6.00%	6.00%
Actual amount	$ 1,864,891	$ 1,790,034
Actual ratio	10.84%	10.70%
Total Risk-Based Capital
Minimum amount	$ 1,375,970	$ 1,337,973
Minimum ratio	8.00%	8.00%
Actual amount	$ 2,142,670	$ 2,029,932
Actual ratio	12.46%	12.14%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 766,355	$ 749,226
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 957,944	$ 936,532
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 1,781,513	$ 1,691,022
Actual ratio	9.30%	9.03%
Common Equity Tier 1 (CET1)
Minimum amount	$ 771,747	$ 750,660
Minimum ratio	4.50%	4.50%
Well capitalized amount	$ 1,114,746	$ 1,084,287
Well capitalized ratio	6.50%	6.50%
Actual amount	$ 1,781,513	$ 1,691,022
Actual ratio	10.39%	10.14%
Tier 1 Risk-Based Capital
Minimum amount	$ 1,028,997	$ 1,000,880
Minimum ratio	6.00%	6.00%
Well capitalized amount	$ 1,371,996	$ 1,334,507
Well capitalized ratio	8.00%	8.00%
Actual amount	$ 1,781,513	$ 1,691,022
Actual ratio	10.39%	10.14%
Total Risk-Based Capital
Minimum amount	$ 1,371,996	$ 1,334,507
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 1,714,994	$ 1,668,133
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 1,942,792	$ 1,843,545
Actual ratio	11.33%	11.05%