Retirement Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Period of employment required to cover employee stock purchase plan	60 days
Percentage of compensation saved by participant for which employer contributes hundred percent	100.00%
Employer matching contribution for first one percent of compensation saved	1.00%
Percentage of compensation saved by participant for which employer contributes fifty percent	50.00%
Employer matching contribution for next five percent of compensation saved	5.00%
Initial saving rate for employees not participating in plan	3.00%
Hancock Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Year of service who have reached 55 years of age	10 years
Year of service who have reached 65 years of age	5 years
Minimum age for increase in per capita cost of health care benefit	55 years
Increase (decrease) in pre- and post-medicare age health costs rate	7.00%
Decrease in ultimate rate over a period of time	5.00%
Whitney 401K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discretionary profit-sharing contribution by employer			$ 2,900,000
Minimum age for increase in per capita cost of health care benefit	65 years
Hancock 401k Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions	$ 7,100,000	$ 7,000,000	$ 6,100,000