Segment Reporting - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Financial information for the Company's operating segments
Net interest income	$ 68,680	$ 50,472	$ 169,192	$ 152,612
Provision for loan losses	750	2,217	3,000	5,117
Noninterest income	32,117	22,563	76,938	60,650
Noninterest expense	76,085	48,175	174,675	145,216
Income before income taxes	23,962	22,643	68,455	62,929
Income taxes	7,742	7,108	21,601	18,944
Net income	16,220	15,535	46,854	43,985
Total assets	7,918,732	5,751,711	7,918,732	5,751,711	$ 5,805,129
Goodwill	452,037	274,658	452,037	274,658	$ 274,706
Operating Segments | Community Banks
Financial information for the Company's operating segments
Net interest income	69,471	51,298	171,310	154,678
Provision for loan losses	749	2,268	3,008	5,158
Noninterest income	26,677	17,547	62,174	46,722
Noninterest expense	71,569	44,129	162,184	133,784
Income before income taxes	23,830	22,448	68,292	62,458
Income taxes	8,039	7,251	22,397	19,397
Net income	15,791	15,197	45,895	43,061
Total assets	7,837,534	5,671,079	7,837,534	5,671,079
Goodwill	449,270	271,891	449,270	271,891
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income	81	65	228	177
Provision for loan losses	0	0	0	0
Noninterest income	2,434	2,261	7,012	6,792
Noninterest expense	1,783	1,656	5,131	4,814
Income before income taxes	732	670	2,109	2,155
Income taxes	289	262	827	844
Net income	443	408	1,282	1,311
Total assets	21,978	18,834	21,978	18,834
Goodwill	2,767	2,767	2,767	2,767
Operating Segments | Wealth Management
Financial information for the Company's operating segments
Net interest income	419	338	1,260	969
Provision for loan losses	1	(51)	(8)	(41)
Noninterest income	2,981	2,357	7,694	6,691
Noninterest expense	2,497	2,177	6,748	6,044
Income before income taxes	902	569	2,214	1,657
Income taxes	0	0	0	0
Net income	902	569	2,214	1,657
Total assets	43,150	46,527	43,150	46,527
Goodwill	0	0	0	0
Operating Segments | Other
Financial information for the Company's operating segments
Net interest income	(1,291)	(1,229)	(3,606)	(3,212)
Provision for loan losses	0	0	0	0
Noninterest income	25	398	58	445
Noninterest expense	236	213	612	574
Income before income taxes	(1,502)	(1,044)	(4,160)	(3,341)
Income taxes	(586)	(405)	(1,623)	(1,297)
Net income	(916)	(639)	(2,537)	(2,044)
Total assets	16,070	15,271	16,070	15,271
Goodwill	$ 0	$ 0	$ 0	$ 0