Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Income Statement Data Abstract
Net interest income	$ 879,580	$ 741,220	$ 707,273
Net intersegment interest income (expense)	0	0	0
Segment net interest income	879,580	741,220	707,273
Noninterest income	355,568	332,680	352,883
Total revenue	1,235,148	1,073,900	1,060,156
Credit provision (a)	0	26,000	70,000
Noninterest expense	821,799	709,133	702,560
Income (loss) before income taxes	413,349	338,767	287,596
Income tax expense (benefit)	79,786	109,503	87,322
Net income	$ 333,562	$ 229,264	$ 200,274
Return on average allocated capital (ROCET1) (b)	13.15%	10.43%	9.86%
Segment Balance Sheet Data
Average earning assets	$ 30,049,793	$ 26,999,884	$ 26,026,661
Average loans	22,718,297	20,592,383	19,650,667
Average deposits	24,072,049	21,923,602	21,005,772
Average allocated capital (CETI)(b)	2,454,919	2,109,459	1,940,391
Allocated goodwill	1,169,023	976,239	971,951
Gain (Loss) on Disposition of Assets for Financial Service Operations	(1,103)	(1,244)	(86)
Operating Segments | Corporate and Commercial Specialty [Member]
Segment Income Statement Data Abstract
Net interest income	457,613	360,789	312,982
Net intersegment interest income (expense)	(56,356)	(3,737)	15,621
Segment net interest income	401,258	357,051	328,603
Noninterest income	52,321	52,297	47,776
Total revenue	453,578	409,348	376,379
Credit provision (a)	44,592	42,298	50,397
Noninterest expense	160,399	156,890	148,493
Income (loss) before income taxes	248,587	210,160	177,489
Income tax expense (benefit)	47,850	71,655	59,261
Net income	$ 200,737	$ 138,505	$ 118,228
Return on average allocated capital (ROCET1) (b)	16.60%	12.39%	11.04%
Segment Balance Sheet Data
Average earning assets	$ 11,852,662	$ 10,820,998	$ 10,178,813
Average loans	11,841,818	10,811,827	10,169,300
Average deposits	8,112,430	6,938,913	5,904,238
Average allocated capital (CETI)(b)	1,209,558	1,117,761	1,070,598
Allocated goodwill	524,525	428,000	428,000
Operating Segments | Community, Consumer and Business [Member]
Segment Income Statement Data Abstract
Net interest income	357,245	316,008	306,913
Net intersegment interest income (expense)	87,737	45,353	43,639
Segment net interest income	444,982	361,361	350,551
Noninterest income	295,647	266,250	277,942
Total revenue	740,629	627,611	628,493
Credit provision (a)	20,083	20,400	24,185
Noninterest expense	542,117	490,908	502,285
Income (loss) before income taxes	178,429	116,303	102,023
Income tax expense (benefit)	37,476	40,706	35,708
Net income	$ 140,953	$ 75,597	$ 66,315
Return on average allocated capital (ROCET1) (b)	21.57%	12.89%	10.53%
Segment Balance Sheet Data
Average earning assets	$ 10,336,105	$ 9,456,549	$ 9,309,028
Average loans	10,332,665	9,452,253	9,307,723
Average deposits	13,623,852	11,711,407	11,451,759
Average allocated capital (CETI)(b)	653,354	586,417	629,540
Allocated goodwill	644,498	548,238	543,951
Operating Segments | Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	64,722	64,423	87,378
Net intersegment interest income (expense)	(31,382)	(41,615)	(59,259)
Segment net interest income	33,341	22,808	28,119
Noninterest income	7,600	14,133	27,165
Total revenue	40,941	36,941	55,284
Credit provision (a)	(64,675)	(36,698)	(4,582)
Noninterest expense	119,283	61,335	51,782
Income (loss) before income taxes	(13,668)	12,304	8,084
Income tax expense (benefit)	(5,540)	(2,858)	(7,647)
Net income	$ (8,128)	$ 15,162	$ 15,731
Return on average allocated capital (ROCET1) (b)	(3.19%)	1.44%	2.84%
Segment Balance Sheet Data
Average earning assets	$ 7,861,026	$ 6,722,337	$ 6,538,820
Average loans	543,814	328,303	173,644
Average deposits	2,335,768	3,273,282	3,649,775
Average allocated capital (CETI)(b)	592,006	405,281	240,253
Allocated goodwill	$ 0	$ 0	$ 0