Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 108,885	$ 108,825	$ 112,800	$ 113,147	$ 115,457	$ 99,439	$ 92,389	$ 89,240	$ 443,657	$ 396,525	$ 336,897
Provision for loan losses	2,950	1,700	900	1,500	1,000	2,250	1,810	1,750	7,050	6,810	7,550
Noninterest income	37,456	37,953	41,960	35,885	36,374	38,053	35,581	33,953	153,254	143,961	132,140
Noninterest expense	95,552	96,500	93,290	88,832	93,313	94,746	79,026	77,944	374,174	345,029	301,618
Income before income taxes	47,839	48,578	60,570	58,700	57,518	40,496	47,134	43,499	215,687	188,647	159,869
Income taxes	9,424	11,132	13,945	13,590	13,098	8,532	10,424	9,673	48,091	41,727	67,681
Net income	38,415	$ 37,446	$ 46,625	$ 45,110	44,420	$ 31,964	$ 36,710	$ 33,826	167,596	146,920	92,188
Total assets	13,400,618				12,934,878				13,400,618	12,934,878	9,829,981
Goodwill	939,683				932,928				939,683	932,928	611,046
Community Banks
Segment Reporting Information [Line Items]
Goodwill	936,916				930,161				936,916	930,161	608,279
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									454,433	406,420	344,499
Provision for loan losses									7,050	6,810	7,550
Noninterest income									129,016	120,559	110,308
Noninterest expense									351,640	323,439	281,698
Income before income taxes									224,759	196,730	165,559
Income taxes									51,292	44,464	70,257
Net income									173,467	152,266	95,302
Total assets	13,280,494				12,828,586				13,280,494	12,828,586	9,717,779
Goodwill	936,916				930,161				936,916	930,161	608,279
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Net interest income									702	484	457
Provision for loan losses									0	0	0
Noninterest income									10,129	9,831	9,530
Noninterest expense									7,574	7,294	6,957
Income before income taxes									3,257	3,021	3,030
Income taxes									876	786	1,184
Net income									2,381	2,235	1,846
Total assets	28,284				25,798				28,284	25,798	26,470
Goodwill	2,767				2,767				2,767	2,767	2,767
Operating Segments | Wealth Management
Segment Reporting Information [Line Items]
Net interest income									1,761	1,297	2,160
Provision for loan losses									0	0	0
Noninterest income									15,598	14,537	12,863
Noninterest expense									13,863	13,336	11,785
Income before income taxes									3,496	2,498	3,238
Income taxes									0	0	0
Net income									3,496	2,498	3,238
Total assets	70,789				60,794				70,789	60,794	61,330
Goodwill	0				0				0	0	0
Other
Segment Reporting Information [Line Items]
Net interest income									(13,239)	(11,676)	(10,219)
Provision for loan losses									0	0	0
Noninterest income									(1,489)	(966)	(561)
Noninterest expense									1,097	960	1,178
Income before income taxes									(15,825)	(13,602)	(11,958)
Income taxes									(4,077)	(3,523)	(3,760)
Net income									(11,748)	(10,079)	(8,198)
Total assets	21,051				19,700				21,051	19,700	24,402
Goodwill	$ 0				$ 0				$ 0	$ 0	$ 0