Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financial information for the Company's operating segments
Net interest income (loss)	$ 89,240	$ 74,015
Provision for loan losses	1,750	1,500
Noninterest income	33,953	32,021
Noninterest expense	77,944	69,309
Income before income taxes	43,499	35,227
Income tax expense (benefit)	9,673	11,255
Net income (loss)	33,826	23,972
Total assets	10,238,313	8,764,711	$ 9,829,981
Goodwill	611,046	470,534	611,046
Community Banks
Financial information for the Company's operating segments
Goodwill	608,279		608,279
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)	91,427	75,956
Provision for loan losses	1,750	1,500
Noninterest income	27,918	26,578
Noninterest expense	72,633	64,221
Income before income taxes	44,962	36,813
Income tax expense (benefit)	10,167	12,110
Net income (loss)	34,795	24,703
Total assets	10,135,478	8,673,576
Goodwill	608,279	467,767
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	106	92
Provision for loan losses	0	0
Noninterest income	2,772	2,549
Noninterest expense	1,731	1,692
Income before income taxes	1,147	949
Income tax expense (benefit)	297	375
Net income (loss)	850	574
Total assets	24,125	24,032
Goodwill	2,767	2,767
Operating Segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	313	487
Provision for loan losses	0	0
Noninterest income	3,527	3,119
Noninterest expense	3,392	2,996
Income before income taxes	448	610
Income tax expense (benefit)	0	0
Net income (loss)	448	610
Total assets	61,800	54,537
Goodwill	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(2,606)	(2,520)
Provision for loan losses	0	0
Noninterest income	(264)	(225)
Noninterest expense	188	400
Income before income taxes	(3,058)	(3,145)
Income tax expense (benefit)	(791)	(1,230)
Net income (loss)	(2,267)	(1,915)
Total assets	16,910	12,566
Goodwill	$ 0	$ 0