Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Financial information for the Company's operating segments
Net interest income (loss)	$ 125,026		$ 130,216		$ 248,316	$ 265,991
Provision for credit losses	3,300		2,000		5,738	8,460
Noninterest income (loss)	38,762		17,226		80,143	54,519
Noninterest expense	111,976		110,165		224,888	219,373
Income (loss) before income taxes	48,512		35,277		97,833	92,677
Income tax expense (benefit)	9,666		6,634		19,578	17,956
Net income (loss)	38,846	$ 39,409	28,643	$ 46,078	78,255	74,721
Total assets	17,510,391		17,224,342		17,510,391	17,224,342	$ 17,360,535
Goodwill	991,665		991,665		991,665	991,665	991,665
Community Banks
Financial information for the Company's operating segments
Goodwill	988,898				988,898		988,898
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)	131,424		136,381		261,110	278,169
Provision for credit losses	3,300		2,000		5,738	8,460
Noninterest income (loss)	29,729		8,747		61,220	37,240
Noninterest expense	104,617		103,282		209,784	205,163
Income (loss) before income taxes	53,236		39,846		106,808	101,786
Income tax expense (benefit)	11,276		8,258		22,640	20,980
Net income (loss)	41,960		31,588		84,168	80,806
Total assets	17,462,835		17,181,988		17,462,835	17,181,988
Goodwill	988,898		988,898		988,898	988,898
Operating segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	461		428		942	714
Provision for credit losses	0		0		0	0
Noninterest income (loss)	2,877		2,859		6,473	6,221
Noninterest expense	2,245		2,070		4,392	4,109
Income (loss) before income taxes	1,093		1,217		3,023	2,826
Income tax expense (benefit)	284		316		785	732
Net income (loss)	809		901		2,238	2,094
Total assets	41,988		37,867		41,988	37,867
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)	16		17		32	36
Provision for credit losses	0		0		0	0
Noninterest income (loss)	6,568		6,050		13,201	11,862
Noninterest expense	4,751		4,407		9,936	9,335
Income (loss) before income taxes	1,833		1,660		3,297	2,563
Income tax expense (benefit)	80		(18)		100	(14)
Net income (loss)	1,753		1,678		3,197	2,577
Total assets	5,043		4,757		5,043	4,757
Goodwill	0		0		0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(6,875)		(6,610)		(13,768)	(12,928)
Provision for credit losses	0		0		0	0
Noninterest income (loss)	(412)		(430)		(751)	(804)
Noninterest expense	363		406		776	766
Income (loss) before income taxes	(7,650)		(7,446)		(15,295)	(14,498)
Income tax expense (benefit)	(1,974)		(1,922)		(3,947)	(3,742)
Net income (loss)	(5,676)		(5,524)		(11,348)	(10,756)
Total assets	525		(270)		525	(270)
Goodwill	$ 0		$ 0		$ 0	$ 0