Segment Reporting - Schedule of Segment Reporting Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Interest income	$ 762,549	$ 592,204	$ 352,558
Interest expense	(51,682)	(70,971)	(82,345)
Net interest income	710,867	521,233	270,213
Provision for loan losses	(54,192)	(38,732)	(65,991)
Noninterest income	252,195	206,427	136,949
Depreciation and amortization	(32,856)	(24,606)	(13,525)
Other noninterest expense	(680,211)	(569,408)	(265,735)
Securities transactions	1,552	(91)
Income before income taxes	197,355	94,823	61,911
Income tax expense	45,613	18,064	9,705
Net income	151,742	76,759	52,206
Goodwill	628,877	651,162	61,631
Total assets	19,464,485	19,774,096	8,138,327
Total interest income from external customers	762,549	592,204	352,558
Hancock [Member]
Segment Reporting Information [Line Items]
Interest income	269,915	195,230	203,222
Interest expense	(22,553)	(39,056)	(61,384)
Net interest income	247,362	156,174	141,838
Provision for loan losses	(21,304)	(17,216)	(37,845)
Noninterest income	78,785	76,846	67,940
Depreciation and amortization	(14,309)	(10,649)	(9,755)
Other noninterest expense	(230,208)	(163,088)	(152,956)
Securities transactions	579	(51)
Income before income taxes	60,905	42,016	9,222
Income tax expense	11,878	6,513	(5,101)
Net income	49,027	35,503	14,323
Goodwill	94,130	23,386	23,386
Total assets	6,308,690	4,934,003	5,247,383
Total interest income from affiliates	4,042	4,364	4,991
Total interest income from external customers	265,873	190,866	198,231
Whitney [Member]
Segment Reporting Information [Line Items]
Interest income	473,664	380,072	132,205
Interest expense	(25,178)	(29,538)	(21,198)
Net interest income	448,486	350,534	111,007
Provision for loan losses	(32,834)	(17,550)	(22,554)
Noninterest income	133,228	96,349	43,331
Depreciation and amortization	(17,515)	(13,123)	(3,003)
Other noninterest expense	(403,935)	(372,034)	(81,665)
Securities transactions	966
Income before income taxes	128,396	44,176	47,116
Income tax expense	30,998	7,584	12,373
Net income	97,398	36,592	34,743
Goodwill	530,265	623,294	33,763
Total assets	13,127,109	14,792,788	2,906,365
Total interest income from affiliates	984	528
Total interest income from external customers	472,680	379,544	132,205
Other [Member]
Segment Reporting Information [Line Items]
Interest income	23,996	21,794	22,122
Interest expense	(8,516)	(6,807)	(4,294)
Net interest income	15,480	14,987	17,828
Provision for loan losses	(54)	(3,966)	(5,592)
Noninterest income	40,219	32,761	25,745
Depreciation and amortization	(1,032)	(834)	(767)
Other noninterest expense	(46,105)	(34,894)	(31,244)
Securities transactions	7	(40)
Income before income taxes	8,515	8,014	5,970
Income tax expense	2,737	3,967	2,433
Net income	5,778	4,047	3,537
Goodwill	4,482	4,482	4,482
Total assets	2,865,346	2,462,281	1,093,565
Total interest income from external customers	23,996	21,794	22,122
Eliminations [Member]
Segment Reporting Information [Line Items]
Interest income	(5,026)	(4,892)	(4,991)
Interest expense	4,565	4,430	4,531
Net interest income	(461)	(462)	(460)
Noninterest income	(37)	471	(67)
Other noninterest expense	37	608	130
Income before income taxes	(461)	617	(397)
Net income	(461)	617	(397)
Total assets	(2,836,660)	(2,414,976)	(1,108,986)
Total interest income from affiliates	$ (5,026)	$ (4,892)	$ (4,991)