Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financial information for the Company's operating segments
Net interest income (loss)	$ 127,383			$ 130,318			$ 393,374	$ 343,462
Provision for credit losses	5,315			9,800			16,275	13,300
Noninterest income (loss)	38,200			41,186			92,719	115,858
Noninterest expense	107,669			101,574			324,542	293,873
Income (loss) before income taxes	52,599			60,130			145,276	152,147
Income tax expense (benefit)	10,766			13,563			28,722	32,355
Net income (loss)	41,833	$ 28,643	$ 46,078	46,567	$ 39,678	$ 33,547	116,554	119,792
Total assets	17,181,621			16,471,099			17,181,621	16,471,099	$ 16,988,176
Goodwill	991,665			946,291			991,665	946,291	991,708
Community Banks
Financial information for the Company's operating segments
Goodwill	988,898						988,898		988,941
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)	133,909			134,528			412,066	356,040
Provision for credit losses	5,315			9,800			16,275	13,300
Noninterest income (loss)	28,679			32,324			66,331	89,359
Noninterest expense	99,791			94,474			302,454	272,594
Income (loss) before income taxes	57,482			62,578			159,668	159,505
Income tax expense (benefit)	12,339			14,811			33,319	36,035
Net income (loss)	45,143			47,767			126,349	123,470
Total assets	17,143,564			16,369,592			17,143,564	16,369,592
Goodwill	988,898			943,524			988,898	943,524
Operating segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	456			98			1,170	286
Provision for credit losses	0			0			0	0
Noninterest income (loss)	3,276			3,123			9,497	8,831
Noninterest expense	2,237			2,190			6,346	6,311
Income (loss) before income taxes	1,495			1,031			4,321	2,806
Income tax expense (benefit)	387			268			1,119	734
Net income (loss)	1,108			763			3,202	2,072
Total assets	39,434			35,761			39,434	35,761
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)	8			794			56	1,813
Provision for credit losses	0			0			0	0
Noninterest income (loss)	6,638			6,132			18,088	18,952
Noninterest expense	5,150			4,553			14,485	13,899
Income (loss) before income taxes	1,496			2,373			3,659	6,866
Income tax expense (benefit)	72			0			58	0
Net income (loss)	1,424			2,373			3,601	6,866
Total assets	5,077			73,704			5,077	73,704
Goodwill	0			0			0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(6,990)			(5,102)			(19,918)	(14,677)
Provision for credit losses	0			0			0	0
Noninterest income (loss)	(393)			(393)			(1,197)	(1,284)
Noninterest expense	491			357			1,257	1,069
Income (loss) before income taxes	(7,874)			(5,852)			(22,372)	(17,030)
Income tax expense (benefit)	(2,032)			(1,516)			(5,774)	(4,414)
Net income (loss)	(5,842)			(4,336)			(16,598)	(12,616)
Total assets	(6,454)			(7,958)			(6,454)	(7,958)
Goodwill	$ 0			$ 0			$ 0	$ 0