Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Income Statement Data Abstract
Net interest income	$ 762,957	$ 835,674	$ 879,580
Net intersegment interest income (expense)	0	0	0
Segment net interest income	762,957	835,674	879,580
Noninterest income	514,056	380,824	355,568
Total revenue	1,277,012	1,216,498	1,235,148
Provision for credit losses	174,006	16,000	0
Noninterest expense	776,034	793,988	821,799
Income (loss) before income taxes	326,972	406,509	413,349
Income tax expense (benefit)	20,200	79,720	79,786
Net income	306,771	326,790	333,562
Segment Balance Sheet Data
Allocated goodwill	1,109,300	1,176,230	1,169,023
Operating Segments | Corporate and Commercial Specialty [Member]
Segment Income Statement Data Abstract
Net interest income	395,135	447,979	458,240
Net intersegment interest income (expense)	10,400	(52,200)	(33,519)
Segment net interest income	405,535	395,779	424,721
Noninterest income	149,456	136,097	132,071
Total revenue	554,991	531,876	556,793
Provision for credit losses	59,780	49,341	42,234
Noninterest expense	209,507	233,655	233,202
Income (loss) before income taxes	285,705	248,879	281,356
Income tax expense (benefit)	53,193	47,480	54,732
Net income	232,512	201,399	226,625
Segment Balance Sheet Data
Allocated goodwill	530,144	530,144	528,832
Operating Segments | Community, Consumer and Business [Member]
Segment Income Statement Data Abstract
Net interest income	295,297	301,563	322,020
Net intersegment interest income (expense)	54,203	93,331	76,876
Segment net interest income	349,500	394,894	398,896
Noninterest income	185,737	223,712	212,711
Total revenue	535,237	618,606	611,607
Provision for credit losses	21,862	18,594	18,500
Noninterest expense	429,447	467,086	463,187
Income (loss) before income taxes	83,928	132,925	129,920
Income tax expense (benefit)	17,625	27,914	27,283
Net income	66,303	105,011	102,637
Segment Balance Sheet Data
Allocated goodwill	579,156	646,086	640,191
Operating Segments | Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	72,525	86,132	99,320
Net intersegment interest income (expense)	(64,603)	(41,130)	(43,357)
Segment net interest income	7,922	45,001	55,963
Noninterest income	178,862	21,015	10,785
Total revenue	186,784	66,017	66,748
Provision for credit losses	92,365	(51,935)	(60,734)
Noninterest expense	137,080	93,247	125,410
Income (loss) before income taxes	(42,661)	24,705	2,073
Income tax expense (benefit)	(50,618)	4,325	(2,228)
Net income	7,957	20,379	4,301
Segment Balance Sheet Data
Allocated goodwill	0	0	0
Business Combination, Acquisition Related Costs	$ 2,000	$ 7,000	$ 29,000