Retirement Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Period of employment for eligibility	60 days
Newly eligible associates initial savings rate	3.00%
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1,363	$ 1,190
Funded status at end of year-net asset (liability)	(22,481)	(22,281)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	16,123	86,123
Funded status at end of year-net asset (liability)	36,274	28,731
Excess of plan assets over the benefit obligation	51,900
Unfunded benefit obligation	15,600
Estimated amounts of actuarial loss that will be amortized from AOCI into net periodic benefit cost over the next year	$ 5,500
Hancock Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum age for increase in per capita cost of health care benefit	55 years
Years of credited service reaching 55 years of age	10 years
Increase (decrease) in pre- and post-medicare age health costs rate	7.00%
Period of assumed health rate decline	4 years
Decrease in ultimate rate over a period of time	5.00%
Whitney 401K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 7,700	$ 7,400	$ 7,100
Minimum age for increase in per capita cost of health care benefit	55 years
Years of credited service reaching 55 years of age	10 years
First 1% Of Contribution Saved [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage	100.00%
Percentage of compensation saved	1.00%
Next 5% Of Contribution Saved [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching percentage	50.00%
Percentage of compensation saved	5.00%