Segment Reporting Selected Segment Income Statement and Balance Sheet Data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Income Statement Data Abstract
Net interest income	$ 166,488	$ 168,703	$ 334,301	$ 333,676
Noninterest income	86,521	72,247	166,597	145,768
Total revenue	253,009	240,950	500,898	479,444
Credit provision	5,000	5,000	9,500	10,000
Noninterest expense	176,816	167,925	351,071	335,583
Income before income taxes	71,193	68,025	140,327	133,861
Income tax expense (benefit)	21,793	21,660	44,255	42,297
Net income	$ 49,400	$ 46,365	$ 96,072	$ 91,564
Return on average allocated capital (ROTICE)	10.50%	9.60%	10.40%	9.50%
Segment Balance Sheet Data
Average earning assets	$ 24,266,367	$ 22,537,515	$ 24,207,523	$ 22,216,791
Average loans	18,188,305	16,646,389	18,002,741	16,406,834
Average deposits	19,626,210	17,172,832	19,342,281	17,082,057
Average allocated capital (TICE)	1,819,819	1,891,766	1,812,061	1,895,629
Corporate and Commercial Specialty [Member]
Segment Income Statement Data Abstract
Net interest income	76,155	74,433	151,846	148,499
Noninterest income	12,305	12,230	24,918	24,083
Total revenue	88,460	86,663	176,764	172,582
Credit provision	9,935	12,915	19,460	25,947
Noninterest expense	34,889	39,792	69,350	75,513
Income before income taxes	43,636	33,956	87,954	71,122
Income tax expense (benefit)	15,061	11,370	30,429	24,378
Net income	$ 28,575	$ 22,586	$ 57,525	$ 46,744
Return on average allocated capital (ROTICE)	11.80%	9.70%	12.10%	10.40%
Segment Balance Sheet Data
Average earning assets	$ 9,422,805	$ 9,188,973	$ 9,321,388	$ 9,020,912
Average loans	9,411,245	9,175,637	9,311,672	9,010,272
Average deposits	5,720,064	5,055,431	5,571,627	5,147,717
Average allocated capital (TICE)	968,690	930,660	955,799	908,844
Community, Consumer, and Business [Member]
Segment Income Statement Data Abstract
Net interest income	87,385	73,091	173,742	145,343
Noninterest income	69,617	57,858	135,131	113,686
Total revenue	157,002	130,949	308,873	259,029
Credit provision	6,592	4,813	13,663	9,760
Noninterest expense	125,474	112,164	244,017	223,363
Income before income taxes	24,936	13,972	51,193	25,906
Income tax expense (benefit)	8,728	4,891	17,918	9,067
Net income	$ 16,208	$ 9,081	$ 33,275	$ 16,839
Return on average allocated capital (ROTICE)	10.20%	6.90%	10.40%	6.40%
Segment Balance Sheet Data
Average earning assets	$ 8,709,691	$ 7,386,355	$ 8,618,054	$ 7,308,806
Average loans	8,709,691	7,386,355	8,618,054	7,308,806
Average deposits	10,862,330	9,731,580	10,693,412	9,636,263
Average allocated capital (TICE)	640,256	526,818	643,796	531,307
Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	2,948	21,179	8,713	39,834
Noninterest income	4,599	2,159	6,548	7,999
Total revenue	7,547	23,338	15,261	47,833
Credit provision	(11,527)	(12,728)	(23,623)	(25,707)
Noninterest expense	16,453	15,969	37,704	36,707
Income before income taxes	2,621	20,097	1,180	36,833
Income tax expense (benefit)	(1,996)	5,399	(4,092)	8,852
Net income	$ 4,617	$ 14,698	$ 5,272	$ 27,981
Return on average allocated capital (ROTICE)	5.80%	12.40%	2.40%	11.30%
Segment Balance Sheet Data
Average earning assets	$ 6,133,871	$ 5,962,187	$ 6,268,081	$ 5,887,073
Average loans	67,369	84,397	73,015	87,756
Average deposits	3,043,816	2,385,821	3,077,242	2,298,077
Average allocated capital (TICE)	$ 210,873	$ 434,288	$ 212,466	$ 455,478