Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Income Statement Data Abstract
Net interest income	$ 155,602	$ 153,160	$ 464,537	$ 461,006
Noninterest income	80,988	68,996	235,385	201,587
Total revenue	236,590	222,156	699,922	662,593
Credit provision	0	4,000	0	51,000
Noninterest expense	169,703	159,480	505,495	478,196
Income before income taxes	66,887	58,676	194,427	133,397
Income tax expense	20,492	17,337	62,082	34,823
Net income	46,395	41,339	132,345	98,574
Return on average allocated capital	9.69%	7.75%	9.40%	5.93%
Segment Balance Sheet Data
Average earning assets	19,659,796	19,530,007	19,473,207	19,420,572
Average loans	14,916,793	13,376,928	14,611,065	13,021,134
Average deposits	15,615,856	14,405,311	15,223,805	14,235,123
Average allocated capital	1,850,610	1,723,954	1,826,270	1,692,991
Commercial Banking Segment [Member]
Segment Income Statement Data Abstract
Net interest income	72,201	64,914	211,855	190,510
Noninterest income	23,669	20,147	65,060	68,085
Total revenue	95,870	85,061	276,915	258,595
Credit provision	11,942	10,062	34,251	29,537
Noninterest expense	53,419	48,032	159,781	143,270
Income before income taxes	30,509	26,967	82,883	85,788
Income tax expense	10,678	9,438	29,009	30,026
Net income	19,831	17,529	53,874	55,762
Return on average allocated capital	10.24%	9.63%	9.48%	10.22%
Segment Balance Sheet Data
Average earning assets	7,757,046	6,434,887	7,410,958	6,244,881
Average loans	7,747,238	6,431,575	7,404,668	6,241,125
Average deposits	4,639,340	3,731,983	4,422,944	3,429,213
Average allocated capital	770,718	723,896	759,913	729,741
Consumer Banking Segment [Member]
Segment Income Statement Data Abstract
Net interest income	73,497	79,192	231,183	243,298
Noninterest income	51,511	48,406	159,951	133,030
Total revenue	125,008	127,598	391,134	376,328
Credit provision	4,845	4,599	14,629	13,310
Noninterest expense	105,181	110,417	317,994	327,109
Income before income taxes	14,982	12,582	58,511	35,909
Income tax expense	5,244	4,404	20,479	12,568
Net income	9,738	8,178	38,032	23,341
Return on average allocated capital	6.69%	5.76%	8.68%	5.72%
Segment Balance Sheet Data
Average earning assets	7,147,934	6,918,760	7,181,048	6,758,489
Average loans	7,147,934	6,918,760	7,181,048	6,758,489
Average deposits	9,426,653	9,558,565	9,437,407	9,531,142
Average allocated capital	579,108	555,499	585,906	545,580
Other Segment [Member]
Segment Income Statement Data Abstract
Net interest income	9,904	9,054	21,499	27,198
Noninterest income	5,808	443	10,374	472
Total revenue	15,712	9,497	31,873	27,670
Credit provision	(16,787)	(10,661)	(48,880)	8,153
Noninterest expense	11,103	1,031	27,720	7,817
Income before income taxes	21,396	19,127	53,033	11,700
Income tax expense	4,570	3,495	12,594	(7,771)
Net income	16,826	15,632	40,439	19,471
Return on average allocated capital	12.33%	7.35%	10.17%	(1.30%)
Segment Balance Sheet Data
Average earning assets	4,754,816	6,176,360	4,881,201	6,417,202
Average loans	21,621	26,593	25,349	21,520
Average deposits	1,549,863	1,114,763	1,363,454	1,274,768
Average allocated capital	$ 500,784	$ 444,559	$ 480,451	$ 417,670