Segment Reporting (Details) $ in Thousands		3 Months Ended						9 Months Ended
		Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment								3
Segment Income Statement Data Abstract
Net interest income		$ 206,365			$ 219,392			$ 635,532	$ 655,625
Net intersegment interest income (expense)		0			0			0	0
Segment net interest income		206,365			219,392			635,532	655,625
Noninterest income		100,850			88,300			287,890	271,522
Total revenue		307,216			307,692			923,422	927,146
Credit provision		2,000			(5,000)			16,000	(1,000)
Noninterest expense		200,930			204,413			590,380	628,636
Income (loss) before income taxes		104,286			108,279			317,042	299,510
Income tax expense (benefit)		20,947			22,349			62,356	54,932
Net income		83,339	$ 84,661	$ 86,686	85,929	$ 89,192	$ 69,456	254,686	244,578
Segment Balance Sheet Data
Allocated goodwill								1,176,230	1,168,922
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income		110,929			113,298			342,486	339,718
Net intersegment interest income (expense)		(17,318)			(13,018)			(60,000)	(36,151)
Segment net interest income		93,612			100,280			282,485	303,567
Noninterest income		13,452			12,280			39,215	39,156
Total revenue		107,063			112,560			321,700	342,723
Credit provision		12,912			11,232			39,713	32,955
Noninterest expense		39,172			41,828			117,982	122,853
Income (loss) before income taxes		54,979			59,500			164,005	186,914
Income tax expense (benefit)		9,670			12,098			30,536	36,978
Net income		45,309			47,402			133,469	149,937
Segment Balance Sheet Data
Allocated goodwill								525,836	524,525
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income		81,517			91,323			254,463	268,137
Net intersegment interest income (expense)		27,651			21,951			76,679	63,301
Segment net interest income		109,167			113,275			331,142	331,438
Noninterest income		81,133			73,838			233,692	224,124
Total revenue		190,300			187,113			564,834	555,562
Credit provision		5,008			5,280			15,007	15,125
Noninterest expense		137,761			139,627			406,984	405,129
Income (loss) before income taxes		47,532			42,206			142,843	135,307
Income tax expense (benefit)		9,982			8,863			30,003	28,415
Net income		37,550			33,343			112,839	106,893
Segment Balance Sheet Data
Allocated goodwill								650,394	644,397
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income		13,919			14,770			38,583	47,770
Net intersegment interest income (expense)		(10,333)			(8,933)			(16,679)	(27,150)
Segment net interest income		3,586			5,837			21,905	20,620
Noninterest income		6,265			2,183			14,983	8,242
Total revenue		9,852			8,019			36,888	28,861
Credit provision		(15,919)			(21,512)			(38,721)	(49,081)
Noninterest expense		23,981			22,959			65,399	100,654
Income (loss) before income taxes		1,790			6,572			10,209	(22,712)
Income tax expense (benefit)		1,295			1,388			1,816	(10,460)
Net income		$ 495			$ 5,185			8,393	(12,252)
Segment Balance Sheet Data
Allocated goodwill								0	0
Business Combinations, Acquisition Related Costs		approximately $2 million			approximately $2 million
Business Combination, Acquisition Related Costs	[1]	$ 1,629			$ 2,271			$ 5,995	$ 29,983

[1] (c) Includes Bank Mutual, Huntington branch, and First Staunton acquisition related costs only.