Segment Reporting - Schedule of Segment Reporting Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Interest income	$ 181,639	$ 189,205	$ 546,560	$ 571,410
Interest expense	(10,109)	(11,949)	(31,836)	(40,407)
Net interest income	171,530	177,256	514,724	531,003
Provision for loan losses	(7,569)	(8,101)	(25,404)	(26,141)
Noninterest income	63,057	62,842	187,141	187,888
Depreciation and amortization	(8,157)	(8,067)	(24,178)	(25,229)
Other noninterest expense	(174,048)	(161,647)	(479,879)	(529,920)
Securities transactions		917		929
Income before income taxes	44,813	63,200	172,404	138,530
Income tax expense	11,611	16,216	43,764	33,747
Net income	33,202	46,984	128,640	104,783
Goodwill	625,675	628,877	625,675	628,877	628,877
Total assets	18,801,846	18,524,130	18,801,846	18,524,130	19,464,485
Total interest income from external customers	181,639	189,205	546,560	571,410
Operating Segments [Member] | Hancock [Member]
Segment Reporting Information [Line Items]
Interest income	66,509	73,558	198,115	201,525
Interest expense	(4,318)	(5,402)	(13,753)	(17,587)
Net interest income	62,191	68,156	184,362	183,938
Provision for loan losses	(7,479)	(4,814)	(15,986)	(7,313)
Noninterest income	18,527	20,205	56,804	59,644
Depreciation and amortization	(3,983)	(3,830)	(11,572)	(10,884)
Other noninterest expense	(65,756)	(59,821)	(173,037)	(174,796)
Securities transactions		94		98
Income before income taxes	3,500	19,990	40,571	50,687
Income tax expense	338	5,433	7,521	11,808
Net income	3,162	14,556	33,050	38,879
Goodwill	94,130	94,130	94,130	94,130
Total assets	6,513,536	6,390,378	6,513,536	6,390,378
Total interest income from affiliates	807	1,010	2,741	3,033
Total interest income from external customers	65,702	72,548	195,374	198,492
Operating Segments [Member] | Whitney [Member]
Segment Reporting Information [Line Items]
Interest income	109,909	110,917	333,322	355,776
Interest expense	(4,583)	(5,669)	(14,162)	(19,915)
Net interest income	105,326	105,248	319,160	335,861
Provision for loan losses	899	(2,353)	(6,016)	(18,696)
Noninterest income	34,366	31,938	97,278	98,122
Depreciation and amortization	(3,868)	(3,981)	(11,698)	(13,596)
Other noninterest expense	(96,334)	(90,087)	(269,735)	(320,985)
Securities transactions		823		824
Income before income taxes	40,389	41,588	128,989	81,530
Income tax expense	10,619	10,130	34,133	18,938
Net income	29,770	31,458	94,856	62,592
Goodwill	527,063	530,265	527,063	530,265
Total assets	12,620,550	12,343,043	12,620,550	12,343,043
Total interest income from affiliates	308	328	748	697
Total interest income from external customers	109,601	110,589	332,574	355,079
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Interest income	6,336	6,068	18,612	17,839
Interest expense	(2,208)	(2,100)	(7,065)	(6,290)
Net interest income	4,128	3,968	11,547	11,549
Provision for loan losses	(989)	(934)	(3,402)	(132)
Noninterest income	10,174	10,722	33,093	30,149
Depreciation and amortization	(306)	(256)	(908)	(749)
Other noninterest expense	(11,968)	(11,761)	(37,141)	(34,166)
Securities transactions				7
Income before income taxes	1,039	1,739	3,189	6,658
Income tax expense	654	653	2,110	3,001
Net income	385	1,086	1,079	3,657
Goodwill	4,482	4,482	4,482	4,482
Total assets	2,747,834	2,737,061	2,747,834	2,737,061
Total interest income from external customers	6,336	6,068	18,612	17,839
Eliminations [Member]
Segment Reporting Information [Line Items]
Interest income	(1,115)	(1,338)	(3,489)	(3,730)
Interest expense	1,000	1,222	3,144	3,385
Net interest income	(115)	(116)	(345)	(345)
Noninterest income	(10)	(23)	(34)	(27)
Other noninterest expense	10	22	34	27
Income before income taxes	(115)	(117)	(345)	(345)
Net income	(115)	(117)	(345)	(345)
Total assets	(3,080,074)	(2,946,352)	(3,080,074)	(2,946,352)
Total interest income from affiliates	$ (1,115)	$ (1,338)	$ (3,489)	$ (3,730)