Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Financial information for the Company's operating segments
Net interest income (loss)	$ 113,515		$ 109,579		$ 213,144	$ 219,227
Provision for credit losses	2,000		0		3,500	0
Noninterest income (loss)	37,214		47,610		74,672	128,647
Noninterest expense	98,194		108,777		192,299	224,712
Income (loss) before income taxes	50,535		48,412		92,017	123,162
Income tax expense (benefit)	10,857		7,545		18,792	24,387
Net income (loss)	39,678	$ 33,547	40,867	$ 57,908	73,225	98,775
Total assets	16,618,101		16,022,386		16,618,101	16,022,386	$ 16,810,311
Goodwill	946,291		939,683		946,291	939,683	939,683
Community Banks
Financial information for the Company's operating segments
Goodwill	943,524				943,524		936,916
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)	117,580		112,780		221,512	225,728
Provision for credit losses	2,000		0		3,500	0
Noninterest income (loss)	28,729		40,149		57,035	113,219
Noninterest expense	91,249		102,426		178,120	212,012
Income (loss) before income taxes	53,060		50,503		96,927	126,935
Income tax expense (benefit)	12,093		8,547		21,224	26,203
Net income (loss)	40,967		41,956		75,703	100,732
Total assets	16,520,685		15,910,027		16,520,685	15,910,027
Goodwill	943,524		936,916		943,524	936,916
Operating segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	95		111		188	218
Provision for credit losses	0		0		0	0
Noninterest income (loss)	2,611		2,475		5,708	5,723
Noninterest expense	2,005		1,987		4,121	3,910
Income (loss) before income taxes	701		599		1,775	2,031
Income tax expense (benefit)	185		153		466	520
Net income (loss)	516		446		1,309	1,511
Total assets	34,264		31,978		34,264	31,978
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)	529		396		1,019	780
Provision for credit losses	0		0		0	0
Noninterest income (loss)	6,315		5,430		12,820	10,601
Noninterest expense	4,591		4,047		9,346	8,148
Income (loss) before income taxes	2,253		1,779		4,493	3,233
Income tax expense (benefit)	0		0		0	0
Net income (loss)	2,253		1,779		4,493	3,233
Total assets	65,709		63,656		65,709	63,656
Goodwill	0		0		0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(4,689)		(3,708)		(9,575)	(7,499)
Provision for credit losses	0		0		0	0
Noninterest income (loss)	(441)		(444)		(891)	(896)
Noninterest expense	349		317		712	642
Income (loss) before income taxes	(5,479)		(4,469)		(11,178)	(9,037)
Income tax expense (benefit)	(1,421)		(1,155)		(2,898)	(2,336)
Net income (loss)	(4,058)		(3,314)		(8,280)	(6,701)
Total assets	(2,557)		16,725		(2,557)	16,725
Goodwill	$ 0		$ 0		$ 0	$ 0