Segment Reporting - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Other intangible assets, net	$ 189,409	$ 211,075
Hancock [Member]
Segment Reporting Information [Line Items]
Other intangible assets, net	20,300	9,400
Whitney [Member]
Segment Reporting Information [Line Items]
Other intangible assets, net	168,900	201,400
Other [Member]
Segment Reporting Information [Line Items]
Other intangible assets, net	200	300
Core Deposit Intangibles [Member]
Segment Reporting Information [Line Items]
Other intangible assets, net	154,700	178,400
Other Identifiable Intangible Assets [Member]
Segment Reporting Information [Line Items]
Other intangible assets, net	$ 34,700	$ 32,700