Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Income Statement Data Abstract
Net interest income	$ 226,362	$ 183,819	$ 436,233	$ 364,093
Noninterest income	92,842	82,410	183,222	162,241
Total revenue	319,204	266,229	619,455	526,334
Credit provision	4,000	12,000	4,000	21,000
Noninterest expense	211,258	176,316	424,223	350,007
Income (loss) before income taxes	103,947	77,913	191,232	155,327
Income tax expense (benefit)	14,754	19,930	32,583	41,074
Net income	$ 89,192	$ 57,983	$ 158,648	$ 114,253
Return on average allocated capital (ROCET1)	14.00%	10.60%	12.70%	10.60%
Segment Balance Sheet Data
Average earning assets	$ 30,412,705	$ 26,744,555	$ 29,850,541	$ 26,543,054
Average loans	23,005,428	20,521,990	22,544,539	20,298,599
Average deposits	23,646,250	21,523,149	23,648,560	21,494,594
Average allocated capital (CET1)	2,488,501	2,099,825	2,439,489	2,080,892
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	107,330	89,871	203,287	179,259
Noninterest income	14,194	12,497	26,876	24,490
Total revenue	121,524	102,368	230,163	203,749
Credit provision	11,126	11,470	21,723	23,050
Noninterest expense	41,775	39,418	81,025	76,897
Income (loss) before income taxes	68,623	51,480	127,415	103,802
Income tax expense (benefit)	13,454	16,363	24,880	34,012
Net income	$ 55,169	$ 35,117	$ 102,535	$ 69,790
Return on average allocated capital (ROCET1)	17.90%	12.50%	17.20%	12.60%
Segment Balance Sheet Data
Average earning assets	$ 12,066,538	$ 10,853,881	$ 11,729,745	$ 10,807,106
Average loans	12,054,347	10,841,858	11,718,236	10,797,831
Average deposits	7,621,977	6,447,190	7,838,409	6,433,870
Average allocated capital (CET1)	1,236,918	1,125,494	1,204,160	1,120,082
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	114,620	90,131	218,163	179,059
Noninterest income	76,250	65,809	150,286	130,679
Total revenue	190,870	155,940	368,449	309,738
Credit provision	4,880	5,764	9,846	10,271
Noninterest expense	138,553	125,242	265,700	241,339
Income (loss) before income taxes	47,437	24,934	92,904	58,128
Income tax expense (benefit)	9,962	8,727	19,510	20,345
Net income	$ 37,475	$ 16,207	$ 73,394	$ 37,783
Return on average allocated capital (ROCET1)	22.70%	11.00%	22.80%	13.10%
Segment Balance Sheet Data
Average earning assets	$ 10,402,680	$ 9,510,571	$ 10,271,021	$ 9,321,564
Average loans	10,399,458	9,508,683	10,267,066	9,319,719
Average deposits	13,736,251	11,574,028	13,418,283	11,456,200
Average allocated capital (CET1)	663,172	588,880	648,032	582,706
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	4,413	3,817	14,783	5,775
Noninterest income	2,399	4,104	6,059	7,072
Total revenue	6,812	7,921	20,842	12,847
Credit provision	(12,006)	(5,234)	(27,569)	(12,321)
Noninterest expense	30,929	11,656	77,498	31,771
Income (loss) before income taxes	(12,111)	1,499	(29,087)	(6,603)
Income tax expense (benefit)	(8,661)	(5,160)	(11,806)	(13,283)
Net income	$ (3,450)	$ 6,659	$ (17,280)	$ 6,680
Return on average allocated capital (ROCET1)	(3.90%)	4.50%	(7.50%)	1.10%
Segment Balance Sheet Data
Average earning assets	$ 7,943,487	$ 6,380,103	$ 7,849,775	$ 6,414,384
Average loans	551,624	171,449	559,238	181,049
Average deposits	2,288,021	3,501,931	2,391,868	3,604,524
Average allocated capital (CET1)	$ 588,411	$ 385,451	$ 587,297	$ 378,104