Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Income Statement Data Abstract
Net interest income	$ 179,515		$ 189,872		$ 355,416	$ 392,814
Net intersegment interest income (expense)	0		0		0	0
Segment net interest income	179,515		189,872		355,416	392,814
Noninterest income(a)	73,443		254,490		168,786	352,796
Total revenue	252,957		444,362		524,202	745,610
Provision for credit losses	(35,004)		61,000		(58,009)	114,001
Noninterest expense	174,475		183,407		349,821	375,598
Income (loss) before income taxes	113,487		199,955		232,389	256,012
Income tax expense (benefit)	22,480		51,238		47,082	61,457
Net income	91,007	$ 94,301	148,718	$ 45,838	185,307	194,555
Segment Balance Sheet Data
Allocated goodwill					1,104,992	1,107,902
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	93,366		98,824		186,527	206,577
Net intersegment interest income (expense)	6,394		6,912		13,078	(3,814)
Segment net interest income	99,760		105,736		199,605	202,764
Noninterest income(a)	38,588		35,115		81,619	73,848
Total revenue	138,348		140,851		281,224	276,612
Provision for credit losses	16,429		13,713		33,938	25,885
Noninterest expense	56,404		53,959		114,129	108,264
Income (loss) before income taxes	65,514		73,179		133,157	142,464
Income tax expense (benefit)	11,947		13,724		24,596	26,664
Net income	53,568		59,456		108,560	115,800
Segment Balance Sheet Data
Allocated goodwill					525,836	530,144
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	70,150		73,120		138,425	148,047
Net intersegment interest income (expense)	13,922		14,317		26,797	32,982
Segment net interest income	84,073		87,437		165,223	181,029
Noninterest income(a)	31,660		54,133		77,788	107,483
Total revenue	115,732		141,570		243,011	288,512
Provision for credit losses	4,565		5,429		9,664	10,537
Noninterest expense	98,260		119,715		195,607	233,491
Income (loss) before income taxes	12,907		16,426		37,740	44,483
Income tax expense (benefit)	2,710		3,450		7,925	9,342
Net income	10,196		12,977		29,815	35,142
Segment Balance Sheet Data
Allocated goodwill					579,156	577,758
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	15,999		17,929		30,464	38,190
Net intersegment interest income (expense)	(20,316)		(21,229)		(39,875)	(29,169)
Segment net interest income	(4,318)		(3,301)		(9,412)	9,021
Noninterest income(a)	3,195		165,242		9,379	171,465
Total revenue	(1,123)		161,941		(32)	180,486
Provision for credit losses	(55,999)		41,858		(101,610)	77,579
Noninterest expense	19,810		9,733		40,086	33,843
Income (loss) before income taxes	35,065		110,350		61,492	69,065
Income tax expense (benefit)	7,823		34,065		14,560	25,451
Net income	$ 27,242		$ 76,285		46,932	43,613
Segment Balance Sheet Data
Allocated goodwill					$ 0	$ 0