Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Income Statement Data Abstract
Net interest income	$ 707,273	$ 676,278	$ 680,967
Noninterest income	352,883	329,357	290,861
Total income	1,060,156	1,005,635	971,828
Credit provision	70,000	37,500	16,000
Noninterest expense	702,560	698,347	679,783
Income before income taxes	287,596	269,788	276,045
Income tax expense (benefit)	87,322	81,487	85,536
Net income	$ 200,274	$ 188,301	$ 190,509
Return on average allocated capital (ROCET1)	9.90%	9.90%	9.90%
Segment Balance Sheet Data
Average earning assets	$ 26,026,661	$ 24,571,087	$ 22,760,128
Average loans	19,650,667	18,252,264	16,838,994
Average deposits	21,005,772	19,903,087	17,647,084
Average allocated capital (CET1)	1,940,391	1,833,597	1,870,609
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	328,603	310,072	296,717
Noninterest income	47,776	46,742	49,213
Total income	376,379	356,814	345,930
Credit provision	50,397	41,913	46,857
Noninterest expense	148,493	141,912	148,476
Income before income taxes	177,489	172,989	150,597
Income tax expense (benefit)	59,261	59,200	50,039
Net income	$ 118,228	$ 113,789	$ 100,558
Return on average allocated capital (ROCET1)	11.00%	11.60%	11.10%
Segment Balance Sheet Data
Average earning assets	$ 10,178,813	$ 9,383,971	$ 8,927,401
Average loans	10,169,300	9,374,191	8,915,498
Average deposits	5,904,238	5,856,530	5,148,195
Average allocated capital (CET1)	1,070,598	977,406	903,500
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	350,551	349,134	310,444
Noninterest income	277,942	265,503	221,430
Total income	628,493	614,637	531,874
Credit provision	24,185	25,614	23,934
Noninterest expense	502,285	492,284	463,235
Income before income taxes	102,023	96,739	44,705
Income tax expense (benefit)	35,708	33,859	15,647
Net income	$ 66,315	$ 62,880	$ 29,058
Return on average allocated capital (ROCET1)	10.50%	9.80%	5.10%
Segment Balance Sheet Data
Average earning assets	$ 9,309,028	$ 8,810,015	$ 7,840,352
Average loans	9,307,723	8,809,673	7,840,352
Average deposits	11,451,759	10,898,602	10,061,495
Average allocated capital (CET1)	629,540	640,181	564,303
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	28,119	17,072	73,806
Noninterest income	27,165	17,112	20,218
Total income	55,284	34,184	94,024
Credit provision	(4,582)	(30,027)	(54,791)
Noninterest expense	51,782	64,151	68,072
Income before income taxes	8,084	60	80,743
Income tax expense (benefit)	(7,647)	(11,572)	19,850
Net income	$ 15,731	$ 11,632	$ 60,893
Return on average allocated capital (ROCET1)	2.80%	2.10%	13.90%
Segment Balance Sheet Data
Average earning assets	$ 6,538,820	$ 6,377,101	$ 5,992,375
Average loans	173,644	68,400	83,144
Average deposits	3,649,775	3,147,955	2,437,394
Average allocated capital (CET1)	$ 240,253	$ 216,010	$ 402,806