Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financial information for the Company's operating segments
Net interest income (loss)	$ 113,147	$ 89,240
Provision for loan losses	1,500	1,750
Noninterest income	35,885	33,953
Noninterest expense	88,832	77,944
Income before income taxes	58,700	43,499
Income tax expense (benefit)	13,590	9,673
Net income (loss)	45,110	33,826
Total assets	12,862,395	10,238,313	$ 12,934,878
Goodwill	932,971	611,046	932,928
Community Banks
Financial information for the Company's operating segments
Goodwill	930,204		930,161
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)	116,058	91,427
Provision for loan losses	1,500	1,750
Noninterest income	29,585	27,918
Noninterest expense	83,313	72,633
Income before income taxes	60,830	44,962
Income tax expense (benefit)	14,286	10,167
Net income (loss)	46,544	34,795
Total assets	12,763,349	10,135,478
Goodwill	930,204	608,279
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	168	106
Provision for loan losses	0	0
Noninterest income	2,879	2,772
Noninterest expense	1,815	1,731
Income before income taxes	1,232	1,147
Income tax expense (benefit)	320	297
Net income (loss)	912	850
Total assets	27,267	24,125
Goodwill	2,767	2,767
Operating Segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	350	313
Provision for loan losses	0	0
Noninterest income	3,659	3,527
Noninterest expense	3,448	3,392
Income before income taxes	561	448
Income tax expense (benefit)	0	0
Net income (loss)	561	448
Total assets	58,971	61,800
Goodwill	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(3,429)	(2,606)
Provision for loan losses	0	0
Noninterest income	(238)	(264)
Noninterest expense	256	188
Income before income taxes	(3,923)	(3,058)
Income tax expense (benefit)	(1,016)	(791)
Net income (loss)	(2,907)	(2,267)
Total assets	12,808	16,910
Goodwill	$ 0	$ 0