Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Income Statement Data Abstract
Net interest income	$ 190,122	$ 178,534	$ 554,215	$ 527,238
Noninterest income	85,895	95,234	248,136	260,594
Total revenue	276,017	273,768	802,351	787,832
Credit provision	5,000	21,000	26,000	55,000
Noninterest expense	177,427	175,314	527,434	523,645
Income (loss) before income taxes	93,590	77,454	248,917	209,187
Income tax expense (benefit)	28,589	23,638	69,663	63,746
Net income	$ 65,001	$ 53,816	$ 179,254	$ 145,441
Return on average allocated capital (ROCET1)	11.70%	10.50%	11.00%	9.70%
Segment Balance Sheet Data
Average earning assets	$ 27,459,795	$ 26,434,163	$ 26,851,992	$ 25,893,509
Average loans	20,899,137	20,052,776	20,500,978	19,541,072
Average deposits	22,441,445	21,404,025	21,813,679	20,758,415
Average allocated capital (CET1)	2,119,675	1,952,616	2,093,962	1,920,895
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	92,356	83,567	271,615	242,800
Noninterest income	12,278	12,623	36,768	35,172
Total revenue	104,634	96,190	308,383	277,972
Credit provision	9,499	11,080	32,549	38,933
Noninterest expense	39,681	37,968	116,578	109,511
Income (loss) before income taxes	55,454	47,142	159,256	129,528
Income tax expense (benefit)	19,070	14,907	53,082	42,623
Net income	$ 36,384	$ 32,235	$ 106,174	$ 86,905
Return on average allocated capital (ROCET1)	12.80%	11.70%	12.70%	10.90%
Segment Balance Sheet Data
Average earning assets	$ 10,923,762	$ 10,441,454	$ 10,846,418	$ 10,097,995
Average loans	10,916,829	10,435,341	10,837,933	10,088,777
Average deposits	7,398,970	6,227,305	6,759,105	5,906,695
Average allocated capital (CET1)	1,125,181	1,091,624	1,121,800	1,063,598
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	90,952	87,274	270,011	257,848
Noninterest income	67,867	78,580	198,546	207,460
Total revenue	158,819	165,854	468,557	465,308
Credit provision	5,046	5,969	15,317	18,357
Noninterest expense	120,241	127,454	361,580	370,714
Income (loss) before income taxes	33,532	32,431	91,660	76,237
Income tax expense (benefit)	11,736	11,351	32,081	26,683
Net income	$ 21,796	$ 21,080	$ 59,579	$ 49,554
Return on average allocated capital (ROCET1)	14.70%	13.20%	13.60%	10.50%
Segment Balance Sheet Data
Average earning assets	$ 9,608,242	$ 9,414,718	$ 9,418,173	$ 9,287,158
Average loans	9,602,098	9,413,401	9,414,880	9,285,848
Average deposits	11,788,606	11,526,639	11,568,220	11,320,106
Average allocated capital (CET1)	588,841	633,392	584,774	631,484
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	6,814	7,693	12,589	26,590
Noninterest income	5,750	4,031	12,822	17,962
Total revenue	12,564	11,724	25,411	44,552
Credit provision	(9,545)	3,951	(21,866)	(2,290)
Noninterest expense	17,505	9,892	49,276	43,420
Income (loss) before income taxes	4,604	(2,119)	(1,999)	3,422
Income tax expense (benefit)	(2,217)	(2,620)	(15,500)	(5,560)
Net income	$ 6,821	$ 501	$ 13,501	$ 8,982
Return on average allocated capital (ROCET1)	4.40%	(2.90%)	2.20%	1.40%
Segment Balance Sheet Data
Average earning assets	$ 6,927,791	$ 6,577,991	$ 6,587,401	$ 6,508,356
Average loans	380,210	204,034	248,165	166,447
Average deposits	3,253,869	3,650,081	3,486,354	3,531,614
Average allocated capital (CET1)	$ 405,653	$ 227,600	$ 387,388	$ 225,813