Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Financial information for the Company's operating segments
Total interest income	$ 220,330	$ 213,179
Total interest expense	86,133	89,889
Net interest income	134,197	123,290
Provision for credit losses	4,750	2,438
Noninterest income (loss)	36,468	41,381
Salaries and employee benefits	71,957	71,470
Net occupancy and equipment	11,754	11,389
Other segment expenses	30,238	30,053
Income (loss) before income taxes	51,966	49,321
Income tax expense (benefit)	10,448	9,912
Net income (loss)	41,518	39,409
Total assets	18,271,381	17,345,741	$ 18,034,868
Goodwill	988,898	991,665	988,898
Community Banks
Financial information for the Company's operating segments
Goodwill	988,898		$ 988,898
Operating segments | Community Banks
Financial information for the Company's operating segments
Total interest income	220,291	212,655
Total interest expense	79,634	82,969
Net interest income	140,657	129,686
Provision for credit losses	4,750	2,438
Noninterest income (loss)	28,845	31,491
Salaries and employee benefits	68,139	66,401
Net occupancy and equipment	11,547	11,103
Other segment expenses	28,172	27,663
Income (loss) before income taxes	56,894	53,572
Income tax expense (benefit)	12,203	11,364
Net income (loss)	44,691	42,208
Total assets	18,266,553	17,303,709
Goodwill	988,898	988,898
Operating segments | Insurance
Financial information for the Company's operating segments
Total interest income		481
Total interest expense		0
Net interest income		481
Provision for credit losses		0
Noninterest income (loss)		3,596
Salaries and employee benefits		1,780
Net occupancy and equipment		90
Other segment expenses		277
Income (loss) before income taxes		1,930
Income tax expense (benefit)		501
Net income (loss)		1,429
Total assets		41,905
Goodwill		2,767
Operating segments | Wealth Management
Financial information for the Company's operating segments
Total interest income	16	16
Total interest expense	0	0
Net interest income	16	16
Provision for credit losses	0	0
Noninterest income (loss)	8,064	6,633
Salaries and employee benefits	3,818	3,289
Net occupancy and equipment	207	196
Other segment expenses	1,568	1,700
Income (loss) before income taxes	2,487	1,464
Income tax expense (benefit)	103	20
Net income (loss)	2,384	1,444
Total assets	5,495	5,409
Goodwill	0	0
Other
Financial information for the Company's operating segments
Total interest income	23	27
Total interest expense	6,499	6,920
Net interest income	(6,476)	(6,893)
Provision for credit losses	0	0
Noninterest income (loss)	(441)	(339)
Salaries and employee benefits	0	0
Net occupancy and equipment	0	0
Other segment expenses	498	413
Income (loss) before income taxes	(7,415)	(7,645)
Income tax expense (benefit)	(1,858)	(1,973)
Net income (loss)	(5,557)	(5,672)
Total assets	(667)	(5,282)
Goodwill	$ 0	$ 0