Acquisitions (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Breakdown of merger expenses
Personnel expense	$ 286,602	$ 142,042	$ 121,449
Equipment expense	17,524	10,569	9,849
Data processing expense	43,069	23,646	19,043
Net occupancy expense	43,220	23,803	20,340
Postage and communications	18,514	11,019	8,474
Professional services expense	69,931	16,447	12,321
Advertising	17,687	7,713	5,597
Insurance expense	7,490	2,010	1,905
Other expense	67,936	29,892	22,391
Whitney Holding Corporation [Member]
Breakdown of merger expenses
Personnel expense	13,960
Equipment expense	552
Data processing expense	3,163
Net occupancy expense	330
Postage and communications	897
Professional services expense	40,902
Printing and supplies	568
Advertising	5,958
Insurance expense	3,177
Other expense	17,255
Total merger-related expenses	86,762
Peoples First Community Bank [Member]
Breakdown of merger expenses
Personnel expense		27	1,760
Equipment expense		57
Data processing expense		944	6
Net occupancy expense		4	118
Postage and communications		60	1
Professional services expense		1,263	1,283
Printing and supplies		194	12
Advertising		113	408
Insurance expense
Other expense		505	94
Total merger-related expenses		$ 3,167	$ 3,682