Segment Reporting - (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financial information for the Company's operating segments
Net interest income	$ 51,670	$ 52,169	$ 100,512	$ 102,140
Provision for loan losses	1,175	1,450	2,250	2,900
Noninterest income	22,917	19,471	44,821	38,087
Noninterest expense	51,176	49,396	98,590	97,041
Income before income taxes	22,236	20,794	44,493	40,286
Income taxes	6,842	5,941	13,859	11,836
Net income	15,394	14,853	30,634	28,450
Total assets	5,899,190	5,826,020	5,899,190	5,826,020	$ 5,805,129
Goodwill	274,698	276,146	274,698	276,146	$ 274,706
Community Banks
Financial information for the Company's operating segments
Net interest income	52,277	52,744	101,870	103,380
Provision for loan losses	1,175	1,501	2,250	2,890
Noninterest income	18,325	15,129	35,461	29,212
Noninterest expense	47,377	45,530	91,068	89,655
Income before income taxes	22,050	20,842	44,013	40,047
Income taxes	7,102	6,168	14,358	12,146
Net income	14,948	14,674	29,655	27,901
Total assets	5,819,329	5,744,942	5,819,329	5,744,942
Goodwill	271,931	273,379	271,931	273,379
Insurance
Financial information for the Company's operating segments
Net interest income	78	49	147	112
Provision for loan losses	0	0	0	0
Noninterest income	2,183	2,138	4,578	4,531
Noninterest expense	1,727	1,684	3,348	3,158
Income before income taxes	534	503	1,377	1,485
Income taxes	218	202	538	582
Net income	316	301	839	903
Total assets	20,438	17,864	20,438	17,864
Goodwill	2,767	2,767	2,767	2,767
Wealth Management
Financial information for the Company's operating segments
Net interest income	395	320	810	631
Provision for loan losses	0	(51)	0	10
Noninterest income	2,385	2,181	4,749	4,297
Noninterest expense	1,904	1,999	3,798	3,867
Income before income taxes	876	553	1,761	1,051
Income taxes	0	0	0	0
Net income	876	553	1,761	1,051
Total assets	43,719	46,259	43,719	46,259
Goodwill	0	0	0	0
Other
Financial information for the Company's operating segments
Net interest income	(1,080)	(944)	(2,315)	(1,983)
Provision for loan losses	0	0	0	0
Noninterest income	24	23	33	47
Noninterest expense	168	183	376	361
Income before income taxes	(1,224)	(1,104)	(2,658)	(2,297)
Income taxes	(478)	(429)	(1,037)	(892)
Net income	(746)	(675)	(1,621)	(1,405)
Total assets	15,704	16,955	15,704	16,955
Goodwill	$ 0	$ 0	$ 0	$ 0