Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Income Statement Data Abstract
Net interest income	$ 183,819	$ 176,717	$ 364,093	$ 348,704
Noninterest income	82,410	82,168	162,241	165,360
Total revenue	266,229	258,885	526,334	514,064
Credit provision	12,000	14,000	21,000	34,000
Noninterest expense	176,316	174,360	350,007	348,331
Income (loss) before income taxes	77,913	70,525	155,327	131,733
Income tax expense (benefit)	19,930	21,434	41,074	40,108
Net income	$ 57,983	$ 49,091	$ 114,253	$ 91,625
Return on average allocated capital (ROCET1)	10.60%	9.90%	10.60%	9.20%
Segment Balance Sheet Data
Average earning assets	$ 26,744,555	$ 25,968,049	$ 26,543,054	$ 25,620,211
Average loans	20,521,990	19,641,985	20,298,599	19,282,408
Average deposits	21,523,149	20,288,953	21,494,594	20,431,966
Average allocated capital (CET1)	2,099,825	1,913,241	2,080,892	1,904,861
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	89,871	80,069	179,259	159,233
Noninterest income	12,497	10,936	24,490	22,549
Total revenue	102,368	91,005	203,749	181,782
Credit provision	11,470	15,114	23,050	27,853
Noninterest expense	39,418	37,140	76,897	71,543
Income (loss) before income taxes	51,480	38,751	103,802	82,386
Income tax expense (benefit)	16,363	13,137	34,012	27,716
Net income	$ 35,117	$ 25,614	$ 69,790	$ 54,670
Return on average allocated capital (ROCET1)	12.50%	9.70%	12.60%	10.50%
Segment Balance Sheet Data
Average earning assets	$ 10,853,881	$ 10,128,726	$ 10,807,106	$ 9,924,378
Average loans	10,841,858	10,115,959	10,797,831	9,913,591
Average deposits	6,447,190	5,570,919	6,433,870	5,744,533
Average allocated capital (CET1)	1,125,494	1,067,203	1,120,082	1,049,431
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	90,131	84,969	179,059	170,574
Noninterest income	65,809	65,132	130,679	128,880
Total revenue	155,940	150,101	309,738	299,454
Credit provision	5,764	6,246	10,271	12,388
Noninterest expense	125,242	121,965	241,339	243,260
Income (loss) before income taxes	24,934	21,890	58,128	43,806
Income tax expense (benefit)	8,727	7,662	20,345	15,332
Net income	$ 16,207	$ 14,228	$ 37,783	$ 28,474
Return on average allocated capital (ROCET1)	11.00%	9.00%	13.10%	9.10%
Segment Balance Sheet Data
Average earning assets	$ 9,510,571	$ 9,325,036	$ 9,321,564	$ 9,222,677
Average loans	9,508,683	9,323,720	9,319,719	9,221,370
Average deposits	11,574,028	11,331,214	11,456,200	11,215,704
Average allocated capital (CET1)	588,880	633,829	582,706	630,520
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	3,817	11,679	5,775	18,897
Noninterest income	4,104	6,100	7,072	13,931
Total revenue	7,921	17,779	12,847	32,828
Credit provision	(5,234)	(7,360)	(12,321)	(6,241)
Noninterest expense	11,656	15,255	31,771	33,528
Income (loss) before income taxes	1,499	9,884	(6,603)	5,541
Income tax expense (benefit)	(5,160)	635	(13,283)	(2,940)
Net income	$ 6,659	$ 9,249	$ 6,680	$ 8,481
Return on average allocated capital (ROCET1)	4.50%	13.40%	1.10%	3.70%
Segment Balance Sheet Data
Average earning assets	$ 6,380,103	$ 6,514,287	$ 6,414,384	$ 6,473,156
Average loans	171,449	202,306	181,049	147,447
Average deposits	3,501,931	3,386,820	3,604,524	3,471,729
Average allocated capital (CET1)	$ 385,451	$ 212,209	$ 378,104	$ 224,910