Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Financial information for the Company's operating segments
Net interest income (loss)	$ 79,603	$ 77,157	$ 153,618	$ 147,211
Provision for loan losses	1,750	1,430	3,250	3,230
Noninterest income	34,265	35,586	66,286	68,888
Noninterest expense	74,841	77,259	144,150	147,073
Income before income taxes	37,277	34,054	72,504	65,796
Income tax expense (benefit)	11,993	11,154	23,248	21,680
Net income (loss)	25,284	22,900	49,256	44,116
Total assets	8,872,272	8,529,566	8,872,272	8,529,566	$ 8,699,851
Goodwill	470,534	470,534	470,534	470,534	470,534
Community Banks
Financial information for the Company's operating segments
Goodwill	467,767		467,767		467,767
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)	81,392	77,564	157,348	148,385
Provision for loan losses	1,750	1,425	3,250	3,238
Noninterest income	28,592	29,172	55,170	56,743
Noninterest expense	70,018	72,448	134,239	137,659
Income before income taxes	38,216	32,863	75,029	64,231
Income tax expense (benefit)	12,712	10,952	24,822	21,591
Net income (loss)	25,504	21,911	50,207	42,640
Total assets	8,776,737	8,429,596	8,776,737	8,429,596
Goodwill	467,767	467,767	467,767	467,767
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	124	88	216	174
Provision for loan losses	0	0	0	0
Noninterest income	2,264	2,280	4,813	5,280
Noninterest expense	1,766	1,741	3,458	3,477
Income before income taxes	622	627	1,571	1,977
Income tax expense (benefit)	238	243	613	773
Net income (loss)	384	384	958	1,204
Total assets	24,746	21,484	24,746	21,484
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)	524	443	1,011	877
Provision for loan losses	0	5	0	(8)
Noninterest income	3,267	3,062	6,386	6,047
Noninterest expense	2,905	2,829	5,901	5,567
Income before income taxes	886	671	1,496	1,365
Income tax expense (benefit)	0	0	0	0
Net income (loss)	886	671	1,496	1,365
Total assets	58,156	51,239	58,156	51,239
Goodwill	0	0	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(2,437)	(938)	(4,957)	(2,225)
Provision for loan losses	0	0	0	0
Noninterest income	142	1,072	(83)	818
Noninterest expense	152	241	552	370
Income before income taxes	(2,447)	(107)	(5,592)	(1,777)
Income tax expense (benefit)	(957)	(41)	(2,187)	(684)
Net income (loss)	(1,490)	(66)	(3,405)	(1,093)
Total assets	12,633	27,247	12,633	27,247
Goodwill	$ 0	$ 0	$ 0	$ 0