Segment Reporting - Financial Information for Operating Segments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financial information for the Company's operating segments
Net interest income (loss)	$ 109,648,000	$ 106,602,000
Provision for loan losses	0	26,350,000
Noninterest income	81,037,000	37,570,000
Noninterest expense	115,935,000	115,041,000
Income (loss) before income taxes	74,750,000	2,781,000
Income tax expense (benefit)	16,842,000	773,000
Net income (loss)	57,908,000	2,008,000
Total assets	15,622,571,000	13,900,550,000	$ 14,929,612,000
Goodwill	939,683,000	939,683,000	939,683,000
Community Banks
Financial information for the Company's operating segments
Goodwill	936,916,000		936,916,000
Insurance
Financial information for the Company's operating segments
Goodwill	2,767,000		$ 2,767,000
Operating segments | Community Banks
Financial information for the Company's operating segments
Net interest income (loss)	112,948,000	108,869,000
Provision for loan losses	0	26,212,000
Noninterest income	73,070,000	30,683,000
Noninterest expense	109,586,000	109,284,000
Income (loss) before income taxes	76,432,000	4,056,000
Income tax expense (benefit)	17,656,000	1,280,000
Net income (loss)	58,776,000	2,776,000
Total assets	15,525,500,000	13,776,076,000
Goodwill	936,916,000	936,916,000
Operating segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	107,000	187,000
Provision for loan losses	0	0
Noninterest income	3,248,000	2,940,000
Noninterest expense	1,923,000	1,886,000
Income (loss) before income taxes	1,432,000	1,241,000
Income tax expense (benefit)	367,000	330,000
Net income (loss)	1,065,000	911,000
Total assets	31,004,000	28,448,000
Goodwill	2,767,000	2,767,000
Operating segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	384,000	441,000
Provision for loan losses	0	138,000
Noninterest income	5,171,000	4,344,000
Noninterest expense	4,101,000	3,945,000
Income (loss) before income taxes	1,454,000	702,000
Income tax expense (benefit)	0	0
Net income (loss)	1,454,000	702,000
Total assets	64,320,000	71,895,000
Goodwill	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(3,791,000)	(2,895,000)
Provision for loan losses	0	0
Noninterest income	(452,000)	(397,000)
Noninterest expense	325,000	(74,000)
Income (loss) before income taxes	(4,568,000)	(3,218,000)
Income tax expense (benefit)	(1,181,000)	(837,000)
Net income (loss)	(3,387,000)	(2,381,000)
Total assets	1,747,000	24,131,000
Goodwill	$ 0	$ 0