Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Financial information for the Company's operating segments
Net interest income (loss)	$ 74,015	$ 70,054
Provision for loan losses	1,500	1,800
Noninterest income	32,021	33,302
Noninterest expense	69,309	69,814
Income before income taxes	35,227	31,742
Income tax expense (benefit)	11,255	10,526
Net income (loss)	23,972	21,216
Total assets	8,764,711	8,146,229	$ 8,699,851
Goodwill	470,534	449,425	470,534
Community Banks
Financial information for the Company's operating segments
Goodwill	467,767		467,767
Insurance
Financial information for the Company's operating segments
Goodwill	2,767		$ 2,767
Operating Segments | Community Banks
Financial information for the Company's operating segments
Net interest income (loss)	75,956	70,821
Provision for loan losses	1,500	1,813
Noninterest income	26,578	27,571
Noninterest expense	64,221	65,211
Income before income taxes	36,813	31,368
Income tax expense (benefit)	12,110	10,639
Net income (loss)	24,703	20,729
Total assets	8,673,576	8,053,379
Goodwill	467,767	446,658
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	92	86
Provision for loan losses	0	0
Noninterest income	2,549	3,000
Noninterest expense	1,692	1,736
Income before income taxes	949	1,350
Income tax expense (benefit)	375	530
Net income (loss)	574	820
Total assets	24,032	23,013
Goodwill	2,767	2,767
Operating Segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	487	434
Provision for loan losses	0	(13)
Noninterest income	3,119	2,985
Noninterest expense	2,996	2,738
Income before income taxes	610	694
Income tax expense (benefit)	0	0
Net income (loss)	610	694
Total assets	54,537	46,645
Goodwill	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(2,520)	(1,287)
Provision for loan losses	0	0
Noninterest income	(225)	(254)
Noninterest expense	400	129
Income before income taxes	(3,145)	(1,670)
Income tax expense (benefit)	(1,230)	(643)
Net income (loss)	(1,915)	(1,027)
Total assets	12,566	23,192
Goodwill	$ 0	$ 0