Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financial information for the Company's operating segments
Net interest income (loss)	$ 75,731	$ 68,612	$ 222,942	$ 169,007
Provision for loan losses	2,650	750	5,880	3,000
Noninterest income (loss)	38,272	32,079	107,160	76,828
Noninterest expense	76,468	75,979	223,541	174,380
Income before income taxes	34,885	23,962	100,681	68,455
Income tax expense (benefit)	11,706	7,742	33,386	21,601
Net income (loss)	23,179	16,220	67,295	46,854
Total assets	8,542,471	7,910,963	8,542,471	7,910,963	$ 7,926,496
Goodwill	470,534	444,268	470,534	444,268	445,871
Community Banks
Financial information for the Company's operating segments
Goodwill	467,767		467,767		443,104
Insurance
Financial information for the Company's operating segments
Goodwill	2,767		2,767		$ 2,767
Operating Segments | Community Banks
Financial information for the Company's operating segments
Net interest income (loss)	77,064	69,404	225,449	171,125
Provision for loan losses	2,655	749	5,893	3,008
Noninterest income (loss)	32,773	26,638	89,515	62,064
Noninterest expense	71,784	71,461	209,442	161,888
Income before income taxes	35,398	23,832	99,629	68,293
Income tax expense (benefit)	12,284	8,040	33,875	22,397
Net income (loss)	23,114	15,792	65,754	45,896
Total assets	8,446,403	7,829,765	8,446,403	7,829,765
Goodwill	467,767	441,501	467,767	441,501
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	85	81	259	228
Provision for loan losses	0	0	0	0
Noninterest income (loss)	2,454	2,434	7,734	7,012
Noninterest expense	1,762	1,783	5,240	5,131
Income before income taxes	777	732	2,753	2,109
Income tax expense (benefit)	301	288	1,074	827
Net income (loss)	476	444	1,679	1,282
Total assets	22,708	21,978	22,708	21,978
Goodwill	2,767	2,767	2,767	2,767
Operating Segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	472	418	1,349	1,260
Provision for loan losses	(5)	1	(13)	(8)
Noninterest income (loss)	3,248	2,981	9,296	7,694
Noninterest expense	2,745	2,497	8,312	6,748
Income before income taxes	980	901	2,346	2,214
Income tax expense (benefit)	0	0	0	0
Net income (loss)	980	901	2,346	2,214
Total assets	51,176	43,150	51,176	43,150
Goodwill	0	0	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(1,890)	(1,291)	(4,115)	(3,606)
Provision for loan losses	0	0	0	0
Noninterest income (loss)	(203)	26	615	58
Noninterest expense	177	238	547	613
Income before income taxes	(2,270)	(1,503)	(4,047)	(4,161)
Income tax expense (benefit)	(879)	(586)	(1,563)	(1,623)
Net income (loss)	(1,391)	(917)	(2,484)	(2,538)
Total assets	22,184	16,070	22,184	16,070
Goodwill	$ 0	$ 0	$ 0	$ 0