Allowance for Credit Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2020
Allowance for loan losses:
Beginning balance	$ 173,106,000	$ 120,185,000	$ 176,144,000	$ 52,162,000
Accounting standards update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Charge-offs	(2,854,000)	(3,566,000)	(8,224,000)	(8,915,000)
Recoveries	2,102,000	1,868,000	4,434,000	6,406,000
Net (charge-offs) recoveries	(752,000)	(1,698,000)	(3,790,000)	(2,509,000)
Provision for credit losses on loans	0	26,900,000	0	53,250,000
Ending balance	172,354,000	145,387,000	172,354,000	145,387,000	$ 52,162,000
Individually evaluated	14,168,000	5,080,000	14,168,000	5,080,000
Collectively evaluated	158,186,000	140,307,000	158,186,000	140,307,000
Loans:
Individually evaluated	40,872,000	23,387,000	40,872,000	23,387,000
Collectively evaluated	10,108,370,000	10,973,917,000	10,108,370,000	10,973,917,000
Gross loans	10,149,242,000	10,997,304,000	10,149,242,000	10,997,304,000		$ 10,933,647,000
Nonaccruing loans with no allowance for credit losses	10,630,000	7,135,000	10,630,000	7,135,000
Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	37,592,000	25,937,000	39,031,000	10,658,000
Charge-offs	(1,184,000)	(1,156,000)	(4,682,000)	(1,549,000)
Recoveries	233,000	108,000	522,000	298,000
Net (charge-offs) recoveries	(951,000)	(1,048,000)	(4,160,000)	(1,251,000)
Provision for credit losses on loans	353,000	5,796,000	2,123,000	9,927,000
Ending balance	36,994,000	30,685,000	36,994,000	30,685,000	10,658,000
Individually evaluated	9,121,000	3,882,000	9,121,000	3,882,000
Collectively evaluated	27,873,000	26,803,000	27,873,000	26,803,000
Loans:
Individually evaluated	14,409,000	9,736,000	14,409,000	9,736,000
Collectively evaluated	1,620,224,000	2,631,862,000	1,620,224,000	2,631,862,000
Gross loans	1,634,633,000	2,641,598,000	1,634,633,000	2,641,598,000
Nonaccruing loans with no allowance for credit losses	2,826,000	720,000	2,826,000	720,000
Real estate – construction:
Allowance for loan losses:
Beginning balance	14,977,000	10,924,000	16,047,000	5,029,000
Charge-offs	0	(532,000)	(52,000)	(532,000)
Recoveries	0	0	13,000	0
Net (charge-offs) recoveries	0	(532,000)	(39,000)	(532,000)
Provision for credit losses on loans	752,000	2,146,000	(279,000)	4,536,000
Ending balance	15,729,000	12,538,000	15,729,000	12,538,000	5,029,000
Individually evaluated	0	0	0	0
Collectively evaluated	15,729,000	12,538,000	15,729,000	12,538,000
Loans:
Individually evaluated	0	0	0	0
Collectively evaluated	1,051,359,000	791,108,000	1,051,359,000	791,108,000
Gross loans	1,051,359,000	791,108,000	1,051,359,000	791,108,000
Nonaccruing loans with no allowance for credit losses	0	0	0	0
Real estate – 1-4 family mortgage:
Allowance for loan losses:
Beginning balance	31,694,000	27,320,000	32,165,000	9,814,000
Charge-offs	(152,000)	(142,000)	(253,000)	(363,000)
Recoveries	401,000	48,000	662,000	136,000
Net (charge-offs) recoveries	249,000	(94,000)	409,000	(227,000)
Provision for credit losses on loans	(640,000)	2,175,000	(1,271,000)	5,500,000
Ending balance	31,303,000	29,401,000	31,303,000	29,401,000	9,814,000
Individually evaluated	228,000	378,000	228,000	378,000
Collectively evaluated	31,075,000	29,023,000	31,075,000	29,023,000
Loans:
Individually evaluated	5,017,000	5,142,000	5,017,000	5,142,000
Collectively evaluated	2,697,074,000	2,783,371,000	2,697,074,000	2,783,371,000
Gross loans	2,702,091,000	2,788,513,000	2,702,091,000	2,788,513,000
Nonaccruing loans with no allowance for credit losses	2,841,000	2,503,000	2,841,000	2,503,000
Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	76,225,000	44,237,000	76,127,000	24,990,000
Charge-offs	(171,000)	0	(232,000)	(2,047,000)
Recoveries	143,000	41,000	314,000	1,740,000
Net (charge-offs) recoveries	(28,000)	41,000	82,000	(307,000)
Provision for credit losses on loans	(1,304,000)	15,783,000	(1,316,000)	31,085,000
Ending balance	74,893,000	60,061,000	74,893,000	60,061,000	24,990,000
Individually evaluated	4,207,000	550,000	4,207,000	550,000
Collectively evaluated	70,686,000	59,511,000	70,686,000	59,511,000
Loans:
Individually evaluated	20,810,000	7,883,000	20,810,000	7,883,000
Collectively evaluated	4,509,359,000	4,402,870,000	4,509,359,000	4,402,870,000
Gross loans	4,530,169,000	4,410,753,000	4,530,169,000	4,410,753,000
Nonaccruing loans with no allowance for credit losses	4,953,000	3,910,000	4,953,000	3,910,000
Lease financing
Allowance for loan losses:
Beginning balance	1,546,000		1,624,000	910,000
Charge-offs	0	0	0	0
Recoveries	14,000	5,000	25,000	10,000
Net (charge-offs) recoveries	14,000	5,000	25,000	10,000
Provision for credit losses on loans	(49,000)	219,000	(138,000)	371,000
Ending balance	1,511,000	1,812,000	1,511,000	1,812,000	910,000
Individually evaluated	0	0	0	0
Collectively evaluated	1,511,000	1,812,000	1,511,000	1,812,000
Loans:
Individually evaluated	0	0	0	0
Collectively evaluated	74,003,000	80,779,000	74,003,000	80,779,000
Gross loans	74,003,000	80,779,000	74,003,000	80,779,000
Nonaccruing loans with no allowance for credit losses	0	0	0	0
Installment Loans to Individuals
Allowance for loan losses:
Beginning balance	11,072,000	10,179,000	11,150,000	761,000
Charge-offs	(1,347,000)	(1,736,000)	(3,005,000)	(4,424,000)
Recoveries	1,311,000	1,666,000	2,898,000	4,222,000
Net (charge-offs) recoveries	(36,000)	(70,000)	(107,000)	(202,000)
Provision for credit losses on loans	888,000	781,000	881,000	1,831,000
Ending balance	11,924,000	10,890,000	11,924,000	10,890,000	761,000
Individually evaluated	612,000	270,000	612,000	270,000
Collectively evaluated	11,312,000	10,620,000	11,312,000	10,620,000
Loans:
Individually evaluated	636,000	626,000	636,000	626,000
Collectively evaluated	156,351,000	283,927,000	156,351,000	283,927,000
Gross loans	156,987,000	284,553,000	156,987,000	284,553,000
Nonaccruing loans with no allowance for credit losses	$ 10,000	$ 2,000	$ 10,000	2,000
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses:
Beginning balance				42,484,000
Ending balance					42,484,000
Cumulative Effect, Period Of Adoption, Adjustment | Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance				11,351,000
Ending balance					11,351,000
Cumulative Effect, Period Of Adoption, Adjustment | Real estate – construction:
Allowance for loan losses:
Beginning balance				3,505,000
Ending balance					3,505,000
Cumulative Effect, Period Of Adoption, Adjustment | Real estate – 1-4 family mortgage:
Allowance for loan losses:
Beginning balance				14,314,000
Ending balance					14,314,000
Cumulative Effect, Period Of Adoption, Adjustment | Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance				4,293,000
Ending balance					4,293,000
Cumulative Effect, Period Of Adoption, Adjustment | Lease financing
Allowance for loan losses:
Beginning balance				521,000
Ending balance					521,000
Cumulative Effect, Period Of Adoption, Adjustment | Installment Loans to Individuals
Allowance for loan losses:
Beginning balance				$ 8,500,000
Ending balance					$ 8,500,000