Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Income Statement Data Abstract
Net interest income	$ 171,987	$ 167,813
Noninterest income	83,192	79,813
Total income	255,179	247,626
Provision for credit losses	20,000	4,500
Noninterest expense	173,971	173,992
Income before income taxes	61,208	69,134
Income tax expense	18,674	22,462
Net income	$ 42,534	$ 46,672
Return on average allocated capital (ROCET1)	8.60%	10.20%
Segment Balance Sheet Data
Average earning assets	$ 25,272,373	$ 24,148,026
Average loans	18,922,830	17,815,115
Average deposits	20,575,174	19,055,196
Average allocated capital (CET1)	1,896,481	1,804,217
Operating Segments [Member] | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	79,164	75,691
Noninterest income	11,613	12,613
Total income	90,777	88,304
Provision for credit losses	12,739	9,526
Noninterest expense	34,403	34,460
Income before income taxes	43,635	44,318
Income tax expense	14,579	15,368
Net income	$ 29,056	$ 28,950
Return on average allocated capital (ROCET1)	11.30%	12.50%
Segment Balance Sheet Data
Average earning assets	$ 9,720,028	$ 9,218,844
Average loans	9,711,221	9,210,992
Average deposits	5,918,341	5,421,541
Average allocated capital (CET1)	1,031,659	942,764
Operating Segments [Member] | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	85,605	86,357
Noninterest income	63,748	65,344
Total income	149,353	151,701
Provision for credit losses	6,142	7,071
Noninterest expense	121,295	118,373
Income before income taxes	21,916	26,257
Income tax expense	7,670	9,190
Net income	$ 14,246	$ 17,067
Return on average allocated capital (ROCET1)	9.10%	10.70%
Segment Balance Sheet Data
Average earning assets	$ 9,120,319	$ 8,525,399
Average loans	9,119,020	8,525,399
Average deposits	11,100,195	10,522,618
Average allocated capital (CET1)	627,211	647,375
Operating Segments [Member] | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	7,218	5,765
Noninterest income	7,831	1,856
Total income	15,049	7,621
Provision for credit losses	1,119	(12,097)
Noninterest expense	18,273	21,159
Income before income taxes	(4,343)	(1,441)
Income tax expense	(3,575)	(2,096)
Net income	$ (768)	$ 655
Return on average allocated capital (ROCET1)	(5.00%)	(1.10%)
Segment Balance Sheet Data
Average earning assets	$ 6,432,026	$ 6,403,783
Average loans	92,589	78,724
Average deposits	3,556,638	3,111,037
Average allocated capital (CET1)	$ 237,611	$ 214,078