Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Reporting Information
Interest income	$ 191,716	$ 82,533
Interest expense	(15,428)	(15,769)
Net interest income	176,288	66,764
Provision for loan losses	(10,015)	(8,822)
Noninterest income	61,494	34,183
Depreciation and amortization	(8,695)	(3,195)
Other noninterest expense	(196,768)	(69,824)
Securities transactions gain	12	(51)
Income before income taxes	22,316	19,055
Income tax (benefit)/expense	3,821	3,727
Net income	18,495	15,328
Goodwill	647,216	61,631
Total assets	19,291,097	8,311,034	19,774,096
Total interest income from affiliates
Total interest income from external customers	191,716	82,533
Hancock [Member]
Segment Reporting Information
Interest income	53,243	47,630
Interest expense	(6,540)	(11,620)
Net interest income	46,703	36,010
Provision for loan losses	2,165	(7,576)
Noninterest income	18,816	17,825
Depreciation and amortization	(3,287)	(2,346)
Other noninterest expense	(51,878)	(39,802)
Securities transactions gain	4	(51)
Income before income taxes	12,523	4,060
Income tax (benefit)/expense	535	(614)
Net income	11,988	4,674
Goodwill	94,130	23,386
Total assets	6,331,361	5,455,793
Total interest income from affiliates	908	1,166
Total interest income from external customers	52,335	46,464
Whitney [Member]
Segment Reporting Information
Interest income	133,749	31,127
Interest expense	(7,846)	(4,197)
Net interest income	125,903	26,930
Provision for loan losses	(13,641)	(672)
Noninterest income	33,691	9,695
Depreciation and amortization	(5,185)	(642)
Other noninterest expense	(134,113)	(21,956)
Securities transactions gain	1
Income before income taxes	6,656	13,355
Income tax (benefit)/expense	1,515	3,715
Net income	5,141	9,640
Goodwill	548,604	33,763
Total assets	12,751,548	2,844,867
Total interest income from affiliates		7
Total interest income from external customers	133,749	31,120
Other [Member]
Segment Reporting Information
Interest income	5,000	4,949
Interest expense	(1,203)	(1,010)
Net interest income	3,797	3,939
Provision for loan losses	1,461	(574)
Noninterest income	8,989	6,670
Depreciation and amortization	(223)	(207)
Other noninterest expense	(10,779)	(8,089)
Securities transactions gain	7
Income before income taxes	3,252	1,739
Income tax (benefit)/expense	1,771	626
Net income	1,481	1,113
Goodwill	4,482	4,482
Total assets	2,683,298	1,277,584
Total interest income from affiliates
Total interest income from external customers	5,000	4,949
Eliminations [Member]
Segment Reporting Information
Interest income	(276)	(1,173)
Interest expense	161	1,058
Net interest income	(115)	(115)
Provision for loan losses
Noninterest income	(2)	(7)
Depreciation and amortization
Other noninterest expense	2	23
Securities transactions gain
Income before income taxes	(115)	(99)
Income tax (benefit)/expense
Net income	(115)	(99)
Goodwill
Total assets	(2,475,110)	(1,267,210)
Total interest income from affiliates	(908)	(1,173)
Total interest income from external customers	$ 632