Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Income Statement Data Abstract
Net interest income	$ 209,871	$ 180,274
Noninterest income	90,380	79,831
Total revenue	300,251	260,105
Credit provision	0	9,000
Noninterest expense	212,965	173,691
Income (loss) before income taxes	87,285	77,414
Income tax expense (benefit)	17,829	21,144
Net income	$ 69,456	$ 56,270
Return on average allocated capital (ROCET1)	11.40%	10.60%
Segment Balance Sheet Data
Average earning assets	$ 29,282,132	$ 26,339,314
Average loans	22,078,529	20,072,725
Average deposits	23,650,898	21,465,722
Average allocated capital (CET1)	2,389,933	2,061,749
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	95,958	89,388
Noninterest income	12,683	11,993
Total revenue	108,641	101,381
Credit provision	10,598	11,580
Noninterest expense	39,250	37,479
Income (loss) before income taxes	58,793	52,322
Income tax expense (benefit)	11,426	17,649
Net income	$ 47,367	$ 34,673
Return on average allocated capital (ROCET1)	16.40%	12.60%
Segment Balance Sheet Data
Average earning assets	$ 11,389,211	$ 10,759,811
Average loans	11,378,390	10,753,314
Average deposits	8,057,246	6,420,401
Average allocated capital (CET1)	1,171,038	1,114,610
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	103,543	88,928
Noninterest income	74,036	64,870
Total revenue	177,579	153,798
Credit provision	4,966	4,507
Noninterest expense	127,144	116,097
Income (loss) before income taxes	45,469	33,194
Income tax expense (benefit)	9,549	11,618
Net income	$ 35,920	$ 21,576
Return on average allocated capital (ROCET1)	23.00%	15.20%
Segment Balance Sheet Data
Average earning assets	$ 10,137,899	$ 9,130,457
Average loans	10,133,202	9,128,656
Average deposits	13,096,782	11,337,064
Average allocated capital (CET1)	632,723	576,464
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	10,370	1,958
Noninterest income	3,661	2,968
Total revenue	14,031	4,926
Credit provision	(15,563)	(7,087)
Noninterest expense	46,571	20,115
Income (loss) before income taxes	(16,977)	(8,102)
Income tax expense (benefit)	(3,146)	(8,123)
Net income	$ (13,831)	$ 21
Return on average allocated capital (ROCET1)	(11.20%)	(2.50%)
Segment Balance Sheet Data
Average earning assets	$ 7,755,022	$ 6,449,046
Average loans	566,936	190,755
Average deposits	2,496,870	3,708,257
Average allocated capital (CET1)	$ 586,172	$ 370,675