Segment Reporting (Details) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment						3
Segment Income Statement Data Abstract
Net interest income		$ 213,619		$ 226,362		$ 429,167	$ 436,233
Net intersegment interest income (expense)		0		0		0	0
Segment net interest income		213,619		226,362		429,167	436,233
Noninterest income		95,837		92,842		187,040	183,222
Total revenue		309,457		319,204		616,206	619,455
Credit provision		8,000		4,000		14,000	4,000
Noninterest Expense		197,779		211,258		389,450	424,223
Income (loss) before income taxes		103,678		103,947		212,756	191,232
Income tax expense (benefit)		19,017		14,754		41,409	32,583
Net income		84,661	$ 86,686	89,192	$ 69,456	171,347	158,648
Segment Balance Sheet Data
Allocated Goodwill - Segment						1,176,019	1,166,665
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income		115,648		121,985		231,557	226,420
Net intersegment interest income (expense)		(20,061)		(14,656)		(42,683)	(23,133)
Segment net interest income		95,587		107,330		188,874	203,287
Noninterest income		14,318		14,194		25,763	26,876
Total revenue		109,904		121,524		214,637	230,163
Credit provision		13,317		11,126		26,802	21,723
Noninterest Expense		40,022		41,775		78,810	81,025
Income (loss) before income taxes		56,566		68,623		109,026	127,415
Income tax expense (benefit)		10,864		13,454		20,866	24,880
Net income		45,702		55,169		88,159	102,535
Segment Balance Sheet Data
Allocated Goodwill - Segment						525,798	523,284
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income		84,874		90,418		172,946	176,813
Net intersegment interest income (expense)		25,586		24,202		49,028	41,350
Segment net interest income		110,461		114,620		221,974	218,163
Noninterest income		78,335		76,250		152,559	150,286
Total revenue		188,796		190,870		374,533	368,449
Credit provision		4,966		4,880		10,000	9,846
Noninterest Expense		138,415		138,553		269,405	265,700
Income (loss) before income taxes		45,415		47,437		95,128	92,904
Income tax expense (benefit)		9,540		9,962		19,983	19,510
Net income		35,874		37,475		75,145	73,394
Segment Balance Sheet Data
Allocated Goodwill - Segment						650,221	643,382
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income		13,097		13,959		24,664	33,000
Net intersegment interest income (expense)		(5,525)		(9,546)		(6,345)	(18,217)
Segment net interest income		7,572		4,413		18,318	14,783
Noninterest income		3,185		2,399		8,718	6,059
Total revenue		10,757		6,812		27,036	20,842
Credit provision		(10,283)		(12,006)		(22,801)	(27,569)
Noninterest Expense	[1]	19,343		30,929		41,236	77,498
Income (loss) before income taxes		1,697		(12,111)		8,602	(29,087)
Income tax expense (benefit)		(1,387)		(8,661)		560	(11,806)
Net income		3,084		(3,450)		8,042	(17,280)
Segment Balance Sheet Data
Allocated Goodwill - Segment						0	0
Business Combination, Acquisition Related Costs	[2]	$ 3,734		$ 7,107		$ 4,366	$ 27,712

[1] (a) For the three months ended June 30, 2019 and 2018, the Risk Management and Shared Services segment includes approximately $4 million and $7 million, respectively, of acquisition related noninterest expense. For the six months ended June 30, 2019 and 2018, the Risk Management and Shared Services segment includes approximately $4 million and $28 million, respectively, of acquisition related noninterest expense.

[2] Includes Bank Mutual and Huntington branch acquisition related costs only.