Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net interest income	$ 108,127	$ 106,286	$ 105,782	$ 106,602	$ 108,885	$ 108,825	$ 112,800	$ 113,147	$ 426,797	$ 443,657	$ 396,525
Provision for loan losses	10,500	23,100	26,900	26,350	2,950	1,700	900	1,500	86,850	7,050	6,810
Noninterest income	62,864	70,928	64,170	37,570	37,456	37,953	41,960	35,885	235,532	153,254	143,961
Noninterest expense	122,152	116,510	118,285	115,041	95,552	96,500	93,290	88,832	471,988	374,174	345,029
Income before income taxes	38,339	37,604	24,767	2,781	47,839	48,578	60,570	58,700	103,491	215,687	188,647
Income taxes	6,818	7,612	4,637	773	9,424	11,132	13,945	13,590	19,840	48,091	41,727
Net income	31,521	$ 29,992	$ 20,130	$ 2,008	38,415	$ 37,446	$ 46,625	$ 45,110	83,651	167,596	146,920
Total assets	14,929,612				13,400,618				14,929,612	13,400,618	12,934,878
Goodwill	939,683				939,683				939,683	939,683	932,928
Community Banks
Segment Reporting Information [Line Items]
Goodwill	936,916				936,916				936,916	936,916	930,161
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									437,101	454,433	406,420
Provision for loan losses									86,850	7,050	6,810
Noninterest income									208,721	129,016	120,559
Noninterest expense									448,475	351,640	323,439
Income before income taxes									110,497	224,759	196,730
Income taxes									22,892	51,292	44,464
Net income									87,605	173,467	152,266
Total assets	14,814,726				13,280,494				14,814,726	13,280,494	12,828,586
Goodwill	936,916				936,916				936,916	936,916	930,161
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Net interest income									566	702	484
Provision for loan losses									0	0	0
Noninterest income									10,403	10,129	9,831
Noninterest expense									7,751	7,574	7,294
Income before income taxes									3,218	3,257	3,021
Income taxes									837	876	786
Net income									2,381	2,381	2,235
Total assets	30,375				28,284				30,375	28,284	25,798
Goodwill	2,767				2,767				2,767	2,767	2,767
Operating Segments | Wealth Management
Segment Reporting Information [Line Items]
Net interest income									1,658	1,761	1,297
Provision for loan losses									0	0	0
Noninterest income									18,061	15,598	14,537
Noninterest expense									14,940	13,863	13,336
Income before income taxes									4,779	3,496	2,498
Income taxes									0	0	0
Net income									4,779	3,496	2,498
Total assets	71,266				70,789				71,266	70,789	60,794
Goodwill	0				0				0	0	0
Other
Segment Reporting Information [Line Items]
Net interest income									(12,528)	(13,239)	(11,676)
Provision for loan losses									0	0	0
Noninterest income									(1,653)	(1,489)	(966)
Noninterest expense									822	1,097	960
Income before income taxes									(15,003)	(15,825)	(13,602)
Income taxes									(3,889)	(4,077)	(3,523)
Net income									(11,114)	(11,748)	(10,079)
Total assets	13,245				21,051				13,245	21,051	19,700
Goodwill	$ 0				$ 0				$ 0	$ 0	$ 0