Stockholders' Equity - Schedule of Compliance with Regulatory Capital Requirements (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Hancock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage capital Actual, Amount	$ 1,844,992	$ 1,777,348
Common equity tier 1 (to risk weighted assets), Actual Amount	1,844,992
Tier 1 capital (to risk weighted assets), Actual, Amount	1,844,992	1,777,348
Total capital (to risk weighted assets), Actual, Amount	$ 2,195,913	$ 1,945,710
Tier 1 leverage capital, Actual, Ratio %	8.55%	9.17%
Common equity tier 1 (to risk weighted assets), Actual, Ratio %	9.96%
Tier 1 capital (to risk weighted assets), Actual, Ratio %	9.96%	11.23%
Total capital (to risk weighted assets), Actual, Ratio %	11.86%	12.30%
Tier 1 leverage capital, Required for Minimum Capital Adequacy, Amount	$ 863,289	$ 581,263
Common equity tier 1 (to risk weighted assets), Required for Minimum Capital Adequacy, Amount	833,216
Tier 1 capital (to risk weighted assets), Required for Minimum Capital Adequacy, Amount	1,110,954	632,898
Total capital (to risk weighted assets), Required for Minimum Capital Adequacy, Amount	$ 1,481,272	$ 1,265,796
Tier 1 leverage capital, Required for Minimum Capital Adequacy, Ratio %	4.00%	3.00%
Common equity tier 1 (to risk weighted assets), Required for Minimum Capital Adequacy, Ratio %	4.50%
Tier 1 capital (to risk weighted assets), Required for Minimum Capital Adequacy, Ratio %	6.00%	4.00%
Total capital (to risk weighted assets), Required for Minimum Capital Adequacy, Ratio %	8.00%	8.00%
Common equity tier 1 (to risk weighted assets), Required To Be Well Capitalized , Amount	$ 1,203,534
Tier 1 leverage capital, To Be Well Capitalized Under Prompt Correct Action Provisions, Amount	1,079,111
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Correct Action Provisions, Amount	1,481,272
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Correct Action Provisions, Amount	$ 1,851,590
Common equity tier 1 (to risk weighted assets), Required To Be Well Capitalized, Ratio %	6.50%
Tier 1 leverage capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio %	5.00%
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio %	8.00%
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio %	10.00%
Whitney Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage capital Actual, Amount	$ 1,965,332	$ 1,756,813
Common equity tier 1 (to risk weighted assets), Actual Amount	1,965,332
Tier 1 capital (to risk weighted assets), Actual, Amount	1,965,332	1,756,813
Total capital (to risk weighted assets), Actual, Amount	$ 2,166,253	$ 1,925,175
Tier 1 leverage capital, Actual, Ratio %	9.16%	9.13%
Common equity tier 1 (to risk weighted assets), Actual, Ratio %	10.64%
Tier 1 capital (to risk weighted assets), Actual, Ratio %	10.64%	11.13%
Total capital (to risk weighted assets), Actual, Ratio %	11.73%	12.20%
Tier 1 leverage capital, Required for Minimum Capital Adequacy, Amount	$ 858,551	$ 577,493
Common equity tier 1 (to risk weighted assets), Required for Minimum Capital Adequacy, Amount	830,985
Tier 1 capital (to risk weighted assets), Required for Minimum Capital Adequacy, Amount	1,107,980	631,220
Total capital (to risk weighted assets), Required for Minimum Capital Adequacy, Amount	$ 1,477,306	$ 1,262,439
Tier 1 leverage capital, Required for Minimum Capital Adequacy, Ratio %	4.00%	3.00%
Common equity tier 1 (to risk weighted assets), Required for Minimum Capital Adequacy, Ratio %	4.50%
Tier 1 capital (to risk weighted assets), Required for Minimum Capital Adequacy, Ratio %	6.00%	4.00%
Total capital (to risk weighted assets), Required for Minimum Capital Adequacy, Ratio %	8.00%	8.00%
Common equity tier 1 (to risk weighted assets), Required To Be Well Capitalized , Amount	$ 1,200,312
Tier 1 leverage capital, To Be Well Capitalized Under Prompt Correct Action Provisions, Amount	1,073,189	$ 962,488
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Correct Action Provisions, Amount	1,477,306	946,829
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Correct Action Provisions, Amount	$ 1,846,633	$ 1,578,049
Common equity tier 1 (to risk weighted assets), Required To Be Well Capitalized, Ratio %	6.50%
Tier 1 leverage capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio %	5.00%	5.00%
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio %	8.00%	6.00%
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio %	10.00%	10.00%