Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Income Statement Data Abstract
Net interest income	$ 175,902	$ 202,942
Net intersegment interest income (expense)	0	0
Segment net interest income	175,902	202,942
Noninterest income(a)	95,343	98,306
Total revenue	271,245	301,248
Provision for credit losses	(23,004)	53,001
Noninterest expense	175,347	192,191
Income (loss) before income taxes	118,903	56,056
Income tax expense (benefit)	24,602	10,219
Net income	94,301	45,838
Segment Balance Sheet Data
Allocated goodwill	1,104,992	1,191,388
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	93,161	107,753
Net intersegment interest income (expense)	6,684	(10,726)
Segment net interest income	99,845	97,028
Noninterest income(a)	43,031	38,733
Total revenue	142,876	135,761
Provision for credit losses	17,509	12,172
Noninterest expense	57,725	54,304
Income (loss) before income taxes	67,642	69,284
Income tax expense (benefit)	12,649	12,940
Net income	54,993	56,344
Segment Balance Sheet Data
Allocated goodwill	525,836	530,144
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	68,275	74,927
Net intersegment interest income (expense)	12,875	18,665
Segment net interest income	81,150	93,592
Noninterest income(a)	46,128	53,350
Total revenue	127,278	146,942
Provision for credit losses	5,099	5,108
Noninterest expense	97,346	113,777
Income (loss) before income taxes	24,834	28,057
Income tax expense (benefit)	5,215	5,892
Net income	19,618	22,165
Segment Balance Sheet Data
Allocated goodwill	579,156	661,244
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	14,465	20,261
Net intersegment interest income (expense)	(19,559)	(7,939)
Segment net interest income	(5,094)	12,322
Noninterest income(a)	6,184	6,223
Total revenue	1,091	18,545
Provision for credit losses	(45,612)	35,720
Noninterest expense	20,275	24,110
Income (loss) before income taxes	26,427	(41,285)
Income tax expense (benefit)	6,737	(8,613)
Net income	19,690	(32,672)
Segment Balance Sheet Data
Allocated goodwill	$ 0	$ 0