Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Consolidated
Tier 1 Leverage
Minimum amount	$ 755,536	$ 751,798
Minimum ratio	4.00%	4.00%
Actual amount	$ 1,777,629	$ 1,790,034
Actual ratio	9.41%	9.52%
Common Equity Tier 1 (CET1)
Minimum amount	$ 757,235	$ 752,610
Minimum ratio	4.50%	4.50%
Actual amount	$ 1,700,817	$ 1,684,097
Actual ratio	10.11%	10.07%
Tier 1 Risk-Based Capital
Minimum amount	$ 1,009,647	$ 1,003,479
Minimum ratio	6.00%	6.00%
Actual amount	$ 1,777,629	$ 1,790,034
Actual ratio	10.56%	10.70%
Total Risk-Based Capital
Minimum amount	$ 1,346,196	$ 1,337,973
Minimum ratio	8.00%	8.00%
Actual amount	$ 2,054,719	$ 2,029,932
Actual ratio	12.21%	12.14%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 753,099	$ 749,226
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 941,373	$ 936,532
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 1,725,728	$ 1,691,022
Actual ratio	9.17%	9.03%
Common Equity Tier 1 (CET1)
Minimum amount	$ 755,278	$ 750,660
Minimum ratio	4.50%	4.50%
Well capitalized amount	$ 1,090,957	$ 1,084,287
Well capitalized ratio	6.50%	6.50%
Actual amount	$ 1,725,728	$ 1,691,022
Actual ratio	10.28%	10.14%
Tier 1 Risk-Based Capital
Minimum amount	$ 1,007,038	$ 1,000,880
Minimum ratio	6.00%	6.00%
Well capitalized amount	$ 1,342,717	$ 1,334,507
Well capitalized ratio	8.00%	8.00%
Actual amount	$ 1,725,278	$ 1,691,022
Actual ratio	10.28%	10.14%
Total Risk-Based Capital
Minimum amount	$ 1,342,717	$ 1,334,507
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 1,678,396	$ 1,668,133
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 1,886,318	$ 1,843,545
Actual ratio	11.24%	11.05%