Segment Reporting Selected Segment Income Statement and Balance Sheet Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Income Statement Data Abstract
Net interest income	$ 172,630	$ 160,509	$ 506,306	$ 478,344
Noninterest income	74,908	70,916	220,676	237,226
Total revenue	247,538	231,425	726,982	715,570
Provision for credit losses	1,000	(800)	11,000	7,800
Noninterest expense	171,853	165,171	507,436	501,482
Income before income taxes	74,685	67,054	208,546	206,288
Income tax expense	24,478	21,396	66,775	65,354
Net income	50,207	45,658	141,771	140,934
Return on average allocated capital	10.40%	9.30%	9.80%	9.80%
Segment Balance Sheet Data
Average earning assets	23,096,717	21,039,467	22,513,323	20,891,857
Average loans	17,140,961	15,724,365	16,654,233	15,634,453
Average deposits	17,873,378	17,609,819	17,348,729	17,288,792
Average allocated capital	1,871,246	1,890,397	1,887,412	1,876,010
Corporate and Commercial Specialty [Member]
Segment Income Statement Data Abstract
Net interest income	71,716	75,677	209,212	222,705
Noninterest income	11,888	11,142	33,711	32,175
Total revenue	83,604	86,819	242,923	254,880
Provision for credit losses	11,074	13,097	34,983	38,161
Noninterest expense	35,044	32,094	103,383	93,806
Income before income taxes	37,486	41,628	104,557	122,913
Income tax expense	12,608	14,569	35,568	43,019
Net income	24,878	27,059	68,989	79,894
Return on average allocated capital	13.30%	14.80%	12.50%	14.70%
Segment Balance Sheet Data
Average earning assets	8,761,870	8,080,676	8,606,965	7,942,744
Average loans	8,750,207	8,074,076	8,595,980	7,933,954
Average deposits	5,092,314	5,124,746	4,841,852	4,964,426
Average allocated capital	744,605	726,588	736,285	724,974
Community, Consumer, and Business [Member]
Segment Income Statement Data Abstract
Net interest income	81,916	85,477	236,687	253,716
Noninterest income	54,601	55,366	170,547	191,236
Total revenue	136,517	140,843	407,234	444,952
Provision for credit losses	6,773	6,041	18,572	18,029
Noninterest expense	122,722	122,450	353,258	364,609
Income before income taxes	7,022	12,352	35,404	62,314
Income tax expense	2,458	4,324	12,391	21,810
Net income	4,564	8,028	23,013	40,504
Return on average allocated capital	3.10%	5.60%	5.40%	9.40%
Segment Balance Sheet Data
Average earning assets	8,310,839	7,647,106	7,973,138	7,696,572
Average loans	8,310,839	7,647,106	7,973,138	7,696,572
Average deposits	10,337,637	10,066,487	10,159,818	10,050,400
Average allocated capital	583,148	567,073	565,588	575,382
Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	18,998	(645)	60,407	1,923
Noninterest income	8,419	4,408	16,418	13,815
Total revenue	27,417	3,763	76,825	15,738
Provision for credit losses	(16,847)	(19,938)	(42,555)	(48,390)
Noninterest expense	14,087	10,627	50,795	43,067
Income before income taxes	30,177	13,074	68,585	21,061
Income tax expense	9,412	2,503	18,816	525
Net income	20,765	10,571	49,769	20,536
Return on average allocated capital	14.20%	6.20%	10.50%	3.90%
Segment Balance Sheet Data
Average earning assets	6,024,008	5,311,685	5,933,220	5,252,541
Average loans	79,915	3,183	85,115	3,927
Average deposits	2,443,427	2,418,586	2,347,059	2,273,966
Average allocated capital	$ 543,493	$ 596,736	$ 585,539	$ 575,654