Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Income Statement Data Abstract
Net interest income	$ 189,872		$ 213,619		$ 392,814	$ 429,167
Net intersegment interest income (expense)	0		0		0	0
Segment net interest income	189,872		213,619		392,814	429,167
Noninterest income	254,490		95,837		352,796	187,040
Total revenue	444,362		309,457		745,610	616,206
Credit provision	61,000		8,000		114,001	14,000
Noninterest expense	183,407		197,779		375,598	389,450
Income (loss) before income taxes	199,955		103,678		256,012	212,756
Income tax expense (benefit)	51,238		19,017		61,457	41,409
Net income	148,718	$ 45,838	84,661	$ 86,686	194,555	171,347
Segment Balance Sheet Data
Allocated goodwill					1,107,902	1,176,019
Gain (Loss) on Disposition of Assets for Financial Service Operations	157,361		871		157,284	1,438
Risk Management and Shared Services
Segment Balance Sheet Data
Gain (Loss) on Disposition of Assets for Financial Service Operations	163,000				163,000
Operating Segments | Corporate and Commercial Specialty
Segment Income Statement Data Abstract
Net interest income	98,824		114,232		206,577	228,162
Net intersegment interest income (expense)	6,889		(13,326)		(3,856)	(28,881)
Segment net interest income	105,713		100,906		202,721	199,281
Noninterest income	30,691		31,267		65,124	58,414
Total revenue	136,405		132,174		267,845	257,695
Credit provision	13,713		12,585		25,885	25,169
Noninterest expense	50,837		56,450		102,098	111,383
Income (loss) before income taxes	71,855		63,139		139,862	121,144
Income tax expense (benefit)	13,446		12,244		26,117	23,411
Net income	58,410		50,895		113,745	97,732
Segment Balance Sheet Data
Allocated goodwill					530,144	530,106
Operating Segments | Community, Consumer, and Business
Segment Income Statement Data Abstract
Net interest income	73,120		77,013		148,047	156,699
Net intersegment interest income (expense)	14,340		22,804		33,025	43,551
Segment net interest income	87,459		99,817		181,072	200,250
Noninterest income	58,557		62,123		116,207	120,398
Total revenue	146,017		161,940		297,279	320,648
Credit provision	5,429		4,626		10,537	9,311
Noninterest expense	122,290		119,694		238,721	232,612
Income (loss) before income taxes	18,298		37,620		48,021	78,725
Income tax expense (benefit)	3,843		7,900		10,084	16,532
Net income	14,455		29,720		37,936	62,193
Segment Balance Sheet Data
Allocated goodwill					577,758	645,913
Operating Segments | Risk Management and Shared Services
Segment Income Statement Data Abstract
Net interest income	17,929		22,375		38,190	44,306
Net intersegment interest income (expense)	(21,229)		(9,478)		(29,169)	(14,671)
Segment net interest income	(3,301)		12,896		9,021	29,635
Noninterest income	165,242		2,447		171,465	8,228
Total revenue	161,941		15,343		180,486	37,863
Credit provision	41,858		(9,211)		77,579	(20,480)
Noninterest expense	10,280		21,634		34,779	45,456
Income (loss) before income taxes	109,802		2,919		68,129	12,887
Income tax expense (benefit)	33,950		(1,127)		25,255	1,466
Net income	75,853		4,047		42,874	11,422
Segment Balance Sheet Data
Allocated goodwill					0	0
Business Combination, Acquisition Related Costs	$ 518		$ 3,734		$ 2,238	$ 4,366