Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income	$ 115,457	$ 99,439	$ 92,389	$ 89,240	$ 93,262	$ 90,017	$ 79,603	$ 74,015	$ 396,525	$ 336,897	$ 300,991
Provision for loan losses	1,000	2,250	1,810	1,750	2,150	2,150	1,750	1,500	6,810	7,550	7,530
Noninterest income	36,374	38,053	35,581	33,953	32,441	33,413	34,265	32,021	143,961	132,140	137,415
Noninterest expense	93,313	94,746	79,026	77,944	76,808	80,660	74,841	69,309	345,029	301,618	295,099
Income before income taxes	57,518	40,496	47,134	43,499	46,745	40,620	37,277	35,227	188,647	159,869	135,777
Income taxes	13,098	8,532	10,424	9,673	30,234	14,199	11,993	11,255	41,727	67,681	44,847
Net income	44,420	$ 31,964	$ 36,710	$ 33,826	16,511	$ 26,421	$ 25,284	$ 23,972	146,920	92,188	90,930
Total assets	12,934,878				9,829,981				12,934,878	9,829,981	8,699,851
Goodwill	932,928				611,046				932,928	611,046	470,534
Community Banks
Segment Reporting Information [Line Items]
Goodwill	930,161				608,279				930,161	608,279	467,767
Insurance
Segment Reporting Information [Line Items]
Goodwill	2,767				2,767				2,767	2,767	2,767
Operating Segments | Community Banks
Segment Reporting Information [Line Items]
Net interest income									406,420	344,499	305,583
Provision for loan losses									6,810	7,550	7,530
Noninterest income									120,559	110,308	114,615
Noninterest expense									323,439	281,698	276,260
Income before income taxes									196,730	165,559	136,408
Income taxes									44,464	70,257	46,352
Net income									152,266	95,302	90,056
Total assets	12,828,586				9,717,779				12,828,586	9,717,779	8,602,022
Goodwill	930,161				608,279				930,161	608,279	467,767
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Net interest income									484	457	350
Provision for loan losses									0	0	0
Noninterest income									9,831	9,530	10,074
Noninterest expense									7,294	6,957	6,873
Income before income taxes									3,021	3,030	3,551
Income taxes									786	1,184	1,385
Net income									2,235	1,846	2,166
Total assets	25,798				26,470				25,798	26,470	23,693
Goodwill	2,767				2,767				2,767	2,767	2,767
Operating Segments | Wealth Management
Segment Reporting Information [Line Items]
Net interest income									1,297	2,160	1,846
Provision for loan losses									0	0	0
Noninterest income									14,537	12,863	12,354
Noninterest expense									13,336	11,785	11,099
Income before income taxes									2,498	3,238	3,101
Income taxes									0	0	0
Net income									2,498	3,238	3,101
Total assets	60,794				61,330				60,794	61,330	54,857
Goodwill	0				0				0	0	0
Other
Segment Reporting Information [Line Items]
Net interest income									(11,676)	(10,219)	(6,788)
Provision for loan losses									0	0	0
Noninterest income									(966)	(561)	372
Noninterest expense									960	1,178	867
Income before income taxes									(13,602)	(11,958)	(7,283)
Income taxes									(3,523)	(3,760)	(2,890)
Net income									(10,079)	(8,198)	(4,393)
Total assets	19,700				24,402				19,700	24,402	19,279
Goodwill	$ 0				$ 0				$ 0	$ 0	$ 0