Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Income Statement Data Abstract
Net interest income	$ 182,150			$ 206,365			$ 574,964	$ 635,532
Net intersegment interest income (expense)	0			0			0	0
Segment net interest income	182,150			206,365			574,964	635,532
Noninterest income	75,545			100,850			428,342	287,890
Total revenue	257,695			307,216			1,003,305	923,422
Credit provision	43,009			2,000			157,009	16,000
Noninterest expense	227,587			200,930			603,184	590,380
Income (loss) before income taxes	(12,900)			104,286			243,112	317,042
Income tax expense (benefit)	(58,114)			20,947			3,342	62,356
Net income	45,214	$ 148,718	$ 45,838	83,339	$ 84,661	$ 86,686	239,769	254,686
Segment Balance Sheet Data
Allocated goodwill							1,107,902	1,176,230
Loss on prepayments of FHLB advances	44,650			0			44,650	0
Tax Benefit from Tax Planning Strategies	49,000						63,000
Risk Management and Shared Services
Segment Balance Sheet Data
Loss on prepayments of FHLB advances							45,000
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	92,033			111,060			298,611	339,222
Net intersegment interest income (expense)	6,937			(12,041)			3,123	(40,863)
Segment net interest income	98,970			99,020			301,734	298,359
Noninterest income	37,405			33,671			111,254	101,135
Total revenue	136,376			132,691			412,987	399,495
Credit provision	15,572			12,248			41,456	37,417
Noninterest expense	52,144			57,946			159,471	174,570
Income (loss) before income taxes	68,660			62,497			212,060	187,508
Income tax expense (benefit)	12,600			11,249			39,461	35,472
Net income	56,060			51,248			172,599	152,036
Segment Balance Sheet Data
Allocated goodwill							530,144	530,144
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	73,644			73,777			221,691	230,476
Net intersegment interest income (expense)	9,231			25,437			42,213	68,930
Segment net interest income	82,875			99,214			263,904	299,406
Noninterest income	32,958			59,934			140,442	171,283
Total revenue	115,833			159,148			404,345	470,688
Credit provision	5,758			4,631			16,296	13,942
Noninterest expense	102,100			118,241			335,591	345,611
Income (loss) before income taxes	7,975			36,277			52,458	111,135
Income tax expense (benefit)	1,675			7,618			11,016	23,338
Net income	6,300			28,658			41,442	87,797
Segment Balance Sheet Data
Allocated goodwill							577,758	646,086
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	16,472			21,528			54,662	65,834
Net intersegment interest income (expense)	(16,167)			(13,396)			(45,336)	(28,067)
Segment net interest income	305			8,131			9,326	37,767
Noninterest income	5,182			7,245			176,646	15,472
Total revenue	5,487			15,376			185,973	53,239
Credit provision	21,679			(14,879)			99,257	(35,359)
Noninterest expense	73,343			24,743			108,122	70,198
Income (loss) before income taxes	(89,535)			5,512			(21,407)	18,400
Income tax expense (benefit)	(72,389)			2,080			(47,135)	3,546
Net income	(17,146)			3,432			25,728	14,854
Segment Balance Sheet Data
Allocated goodwill							0	0
Business Combination, Acquisition Related Costs	$ 218			$ 1,629			$ 2,457	$ 5,995