Retirement Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Number of consecutive year level of compensation for non qualified benefit pension plan	5 years
Number of final years of employment for non qualified benefit pension plan	10 years
Period of employment required to cover employee stock purchase plan	60 days
Minimum service period must have completed to become vested in the Company's contributions	3 years
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%
S&P 500 Index [Member]
Defined Benefit Plan Disclosure [Line Items]
Return on investment	55.00%
Barclays Intermediate Aggregate Index [Member]
Defined Benefit Plan Disclosure [Line Items]
Return on investment	45.00%
Hancock Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss included in accumulated other comprehensive income	$ 6,000,000
Number of shares of parent company included in plan assets	16,375	16,375
Value of Shares of Parent Company included in Plan Assets	500,000	500,000
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	7.50%
Decrease in ultimate rate over a period of time	5.00%
Whitney Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of compensation on base percentage for participating in plan	4.00%
Discretionary profit-sharing contribution by employer	2,900,000	1,600,000
Minimum age for increase in per capita cost of health care benefit	65 years
Whitney & Hancock Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions	6,100,000	4,500,000	2,000,000
Defined Benefit Plan-Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated contributions	16,000,000
Defined Benefit Plan-Pension [Member] | Hancock Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents	$ 25,000,000
Defined Contribution Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of savings for calculating each employee participation in plan	50.00%
Maximum percentage of compensation on base percentage for participating in plan	6.00%