Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Income Statement Data Abstract
Net interest income	$ 183,675			$ 182,150			$ 539,092	$ 574,964
Net intersegment interest income (expense)	0			0			0	0
Segment net interest income	183,675			182,150			539,092	574,964
Noninterest income(a)	82,076			75,545			250,862	428,342
Total revenue	265,752			257,695			789,954	1,003,305
Provision for credit losses	(24,010)			43,009			(82,018)	157,009
Noninterest expense	177,892			227,587			527,713	603,184
Income (loss) before income taxes	111,870			(12,900)			344,259	243,112
Income tax expense (benefit)	23,060			(58,114)			70,142	3,342
Net income	88,809	$ 91,007	$ 94,301	45,214	$ 148,718	$ 45,838	274,117	239,769
Segment Balance Sheet Data
Allocated goodwill							1,104,992	1,107,902
Loss on prepayments of FHLB advances	0			44,650			0
Risk Management and Shared Services
Segment Balance Sheet Data
Loss on prepayments of FHLB advances							44,650
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	93,768			92,033			280,295	298,611
Net intersegment interest income (expense)	5,884			6,937			18,962	3,123
Segment net interest income	99,652			98,970			299,257	301,734
Noninterest income(a)	43,228			37,405			124,847	111,254
Total revenue	142,881			136,376			424,104	412,987
Provision for credit losses	14,864			15,572			48,803	41,456
Noninterest expense	58,652			52,635			172,781	160,899
Income (loss) before income taxes	69,364			68,169			202,521	210,633
Income tax expense (benefit)	12,617			12,497			37,213	39,161
Net income	56,747			55,672			165,307	171,472
Segment Balance Sheet Data
Allocated goodwill							525,836	530,144
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	70,860			73,644			209,285	221,691
Net intersegment interest income (expense)	12,907			9,231			39,705	42,213
Segment net interest income	83,767			82,875			248,990	263,904
Noninterest income(a)	35,771			32,958			113,558	140,442
Total revenue	119,538			115,833			362,548	404,345
Provision for credit losses	4,233			5,758			13,897	16,296
Noninterest expense	94,762			102,139			290,443	335,675
Income (loss) before income taxes	20,543			7,936			58,209	52,374
Income tax expense (benefit)	4,314			1,667			12,224	10,999
Net income	16,230			6,269			45,985	41,376
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	19,047			16,472			49,511	54,662
Net intersegment interest income (expense)	(18,791)			(16,167)			(58,666)	(45,336)
Segment net interest income	256			305			(9,155)	9,326
Noninterest income(a)	3,077			5,182			12,457	176,646
Total revenue	3,333			5,487			3,301	185,973
Provision for credit losses	(43,107)			21,679			(144,717)	99,257
Noninterest expense	24,478			72,813			64,490	106,610
Income (loss) before income taxes	21,962			(89,005)			83,529	(19,895)
Income tax expense (benefit)	6,129			(72,278)			20,705	(46,817)
Net income	$ 15,833			$ (16,727)			62,824	26,922
Segment Balance Sheet Data
Allocated goodwill							$ 0	$ 0