Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Income Statement Data Abstract
Net interest income	$ 180,274	$ 171,987
Noninterest income	79,831	83,192
Total revenue	260,105	255,179
Credit provision	9,000	20,000
Noninterest expense	173,691	173,971
Income (loss) before income taxes	77,414	61,208
Income tax expense (benefit)	21,144	18,674
Net income	$ 56,270	$ 42,534
Return on average allocated capital (ROCET1)	10.60%	8.60%
Segment Balance Sheet Data
Average earning assets	$ 26,339,314	$ 25,272,373
Average loans	20,072,725	18,922,830
Average deposits	21,465,722	20,575,174
Average allocated capital (CET1)	2,061,749	1,896,481
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	89,388	79,164
Noninterest income	11,993	11,613
Total revenue	101,381	90,777
Credit provision	11,580	12,739
Noninterest expense	37,479	34,403
Income (loss) before income taxes	52,322	43,635
Income tax expense (benefit)	17,649	14,579
Net income	$ 34,673	$ 29,056
Return on average allocated capital (ROCET1)	12.60%	11.30%
Segment Balance Sheet Data
Average earning assets	$ 10,759,811	$ 9,720,028
Average loans	10,753,314	9,711,221
Average deposits	6,420,401	5,918,341
Average allocated capital (CET1)	1,114,610	1,031,659
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	88,928	85,605
Noninterest income	64,870	63,748
Total revenue	153,798	149,353
Credit provision	4,507	6,142
Noninterest expense	116,097	121,295
Income (loss) before income taxes	33,194	21,916
Income tax expense (benefit)	11,618	7,670
Net income	$ 21,576	$ 14,246
Return on average allocated capital (ROCET1)	15.20%	9.10%
Segment Balance Sheet Data
Average earning assets	$ 9,130,457	$ 9,120,319
Average loans	9,128,656	9,119,020
Average deposits	11,337,064	11,100,195
Average allocated capital (CET1)	576,464	627,211
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	1,958	7,218
Noninterest income	2,968	7,831
Total revenue	4,926	15,049
Credit provision	(7,087)	1,119
Noninterest expense	20,115	18,273
Income (loss) before income taxes	(8,102)	(4,343)
Income tax expense (benefit)	(8,123)	(3,575)
Net income	$ 21	$ (768)
Return on average allocated capital (ROCET1)	(2.50%)	(5.00%)
Segment Balance Sheet Data
Average earning assets	$ 6,449,046	$ 6,432,026
Average loans	190,755	92,589
Average deposits	3,708,257	3,556,638
Average allocated capital (CET1)	$ 370,675	$ 237,611