Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Financial information for the Company's operating segments
Net interest income	$ 77,157	$ 51,614	$ 147,211	$ 100,395
Provision for loan losses	1,430	1,175	3,230	2,250
Noninterest income	35,586	22,879	68,888	44,749
Noninterest expense	77,259	51,082	147,073	98,401
Income before income taxes	34,054	22,236	65,796	44,493
Income taxes	11,154	6,842	21,680	13,859
Net income (loss)	22,900	15,394	44,116	30,634
Total assets	8,529,566	5,899,190	8,529,566	5,899,190	$ 7,926,496
Goodwill	470,534	274,698	470,534	274,698	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	77,564	52,205	148,385	101,721
Provision for loan losses	1,425	1,181	3,238	2,259
Noninterest income	29,172	18,325	56,743	35,426
Noninterest expense	72,448	47,044	137,659	90,427
Income before income taxes	32,863	22,305	64,231	44,461
Income taxes	10,952	7,103	21,591	14,359
Net income (loss)	21,911	15,202	42,640	30,102
Total assets	8,429,596	5,818,191	8,429,596	5,818,191
Goodwill	467,767	271,931	467,767	271,931
Operating Segments | Insurance
Financial information for the Company's operating segments
Net interest income	88	78	174	147
Provision for loan losses	0	0	0	0
Noninterest income	2,280	2,183	5,280	4,578
Noninterest expense	1,741	1,727	3,477	3,348
Income before income taxes	627	534	1,977	1,377
Income taxes	243	218	773	538
Net income (loss)	384	316	1,204	839
Total assets	21,484	20,438	21,484	20,438
Goodwill	2,767	2,767	2,767	2,767
Operating Segments | Wealth Management
Financial information for the Company's operating segments
Net interest income	443	412	877	842
Provision for loan losses	5	(6)	(8)	(9)
Noninterest income	3,062	2,348	6,047	4,713
Noninterest expense	2,829	2,144	5,567	4,251
Income before income taxes	671	622	1,365	1,313
Income taxes	0	0	0	0
Net income (loss)	671	622	1,365	1,313
Total assets	51,239	43,719	51,239	43,719
Goodwill	0	0	0	0
Operating Segments | Other
Financial information for the Company's operating segments
Net interest income	(938)	(1,081)	(2,225)	(2,315)
Provision for loan losses	0	0	0	0
Noninterest income	1,072	23	818	32
Noninterest expense	241	167	370	375
Income before income taxes	(107)	(1,225)	(1,777)	(2,658)
Income taxes	(41)	(479)	(684)	(1,038)
Net income (loss)	(66)	(746)	(1,093)	(1,620)
Total assets	27,247	16,842	27,247	16,842
Goodwill	$ 0	$ 0	$ 0	$ 0