Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Income Statement Data Abstract
Net interest income	$ 835,674	$ 879,580	$ 741,220
Net intersegment interest income (expense)	0	0	0
Segment net interest income	835,674	879,580	741,220
Noninterest income	380,824	355,568	332,680
Total revenue	1,216,498	1,235,148	1,073,900
Credit provision	16,000	0	26,000
Noninterest expense	793,988	821,799	709,133
Income (loss) before income taxes	406,509	413,349	338,767
Income tax expense (benefit)	79,720	79,786	109,503
Net income	326,790	333,562	229,264
Segment Balance Sheet Data
Allocated goodwill	1,176,230	1,169,023	976,239
Operating Segments | Corporate and Commercial Specialty [Member]
Segment Income Statement Data Abstract
Net interest income	450,532	457,613	360,789
Net intersegment interest income (expense)	(76,064)	(56,356)	(3,737)
Segment net interest income	374,467	401,258	357,051
Noninterest income	53,282	52,321	52,297
Total revenue	427,749	453,578	409,348
Credit provision	52,382	44,592	42,298
Noninterest expense	156,348	160,399	156,890
Income (loss) before income taxes	219,019	248,587	210,160
Income tax expense (benefit)	41,209	47,850	71,655
Net income	177,809	200,737	138,505
Segment Balance Sheet Data
Allocated goodwill	525,836	524,525	428,000
Operating Segments | Community, Consumer and Business [Member]
Segment Income Statement Data Abstract
Net interest income	332,850	357,245	316,008
Net intersegment interest income (expense)	103,468	87,737	45,353
Segment net interest income	436,318	444,982	361,361
Noninterest income	307,750	295,647	266,250
Total revenue	744,067	740,629	627,611
Credit provision	20,043	20,083	20,400
Noninterest expense	547,423	541,771	490,567
Income (loss) before income taxes	176,601	178,775	116,645
Income tax expense (benefit)	37,105	37,543	40,826
Net income	139,496	141,232	75,819
Segment Balance Sheet Data
Allocated goodwill	650,394	644,498	548,238
Operating Segments | Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	52,292	64,722	64,423
Net intersegment interest income (expense)	(27,403)	(31,382)	(41,615)
Segment net interest income	24,889	33,341	22,808
Noninterest income	19,793	7,600	14,133
Total revenue	44,682	40,941	36,941
Credit provision	(56,425)	(64,675)	(36,698)
Noninterest expense	90,217	119,629	61,677
Income (loss) before income taxes	10,890	(14,013)	11,962
Income tax expense (benefit)	1,405	(5,606)	(2,978)
Net income	9,484	(8,407)	14,941
Segment Balance Sheet Data
Allocated goodwill	0	0	$ 0
Business Combination, Acquisition Related Costs	7,000	$ 29,000
Gain (Loss) on Disposition of Assets for Financial Service Operations	$ 2,000