Segment Reporting (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) segment	Sep. 30, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Segment Income Statement Data Abstract
Net interest income	$ 178,534	$ 170,509	$ 527,238	$ 504,810
Noninterest income	95,234	80,065	260,594	246,360
Total revenue	273,768	250,574	787,832	751,170
Credit provision	21,000	8,000	55,000	17,500
Noninterest expense	175,314	171,585	523,645	522,354
Income before income taxes	77,454	70,989	209,187	211,316
Income tax expense (benefit)	23,638	21,551	63,746	65,806
Net income	$ 53,816	$ 49,438	$ 145,441	$ 145,510
Return on average allocated capital (ROCET1)	10.50%	10.20%	9.70%	10.30%
Segment Balance Sheet Data
Average earning assets	$ 26,434,163	$ 24,834,343	$ 25,893,509	$ 24,418,759
Average loans	20,052,776	18,452,749	19,541,072	18,154,392
Average deposits	21,404,025	20,293,599	20,758,415	19,662,872
Average allocated capital (CET1)	1,952,616	1,837,436	1,920,895	1,820,612
Operating Segments [Member] | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	83,567	78,283	242,800	230,130
Noninterest income	12,623	11,305	35,172	36,222
Total revenue	96,190	89,588	277,972	266,352
Credit provision	11,080	10,851	38,933	30,312
Noninterest expense	37,968	37,293	109,511	106,643
Income before income taxes	47,142	41,444	129,528	129,397
Income tax expense (benefit)	14,907	13,955	42,623	44,384
Net income	$ 32,235	$ 27,489	$ 86,905	$ 85,013
Return on average allocated capital (ROCET1)	11.70%	11.00%	10.90%	11.80%
Segment Balance Sheet Data
Average earning assets	$ 10,441,454	$ 9,475,469	$ 10,097,995	$ 9,373,312
Average loans	10,435,341	9,466,761	10,088,777	9,363,936
Average deposits	6,227,305	6,044,306	5,906,695	5,730,918
Average allocated capital (CET1)	1,091,624	988,283	1,063,598	966,746
Operating Segments [Member] | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	87,274	88,209	257,848	261,951
Noninterest income	78,580	64,879	207,460	199,753
Total revenue	165,854	153,088	465,308	461,704
Credit provision	5,969	5,963	18,357	19,625
Noninterest expense	127,454	122,361	370,714	366,121
Income before income taxes	32,431	24,764	76,237	75,958
Income tax expense (benefit)	11,351	8,667	26,683	26,585
Net income	$ 21,080	$ 16,097	$ 49,554	$ 49,373
Return on average allocated capital (ROCET1)	13.20%	10.10%	10.50%	10.30%
Segment Balance Sheet Data
Average earning assets	$ 9,414,718	$ 8,917,831	$ 9,287,158	$ 8,719,078
Average loans	9,413,401	8,917,831	9,285,848	8,719,078
Average deposits	11,526,639	10,969,172	11,320,106	10,786,342
Average allocated capital (CET1)	633,392	632,878	631,484	640,116
Operating Segments [Member] | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	7,693	4,017	26,590	12,729
Noninterest income	4,031	3,881	17,962	10,385
Total revenue	11,724	7,898	44,552	23,114
Credit provision	3,951	(8,814)	(2,290)	(32,437)
Noninterest expense	9,892	11,931	43,420	49,590
Income before income taxes	(2,119)	4,781	3,422	5,961
Income tax expense (benefit)	(2,620)	(1,071)	(5,560)	(5,163)
Net income	$ 501	$ 5,852	$ 8,982	$ 11,124
Return on average allocated capital (ROCET1)	(2.90%)	6.70%	1.40%	3.90%
Segment Balance Sheet Data
Average earning assets	$ 6,577,991	$ 6,441,043	$ 6,508,356	$ 6,326,369
Average loans	204,034	68,157	166,447	71,378
Average deposits	3,650,081	3,280,121	3,531,614	3,145,612
Average allocated capital (CET1)	$ 227,600	$ 216,275	$ 225,813	$ 213,750