Allowance for Credit Losses - Changes in the Allowance for Credit Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for loan losses:
Beginning balance	$ 52,162	$ 49,026	$ 46,211
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Charge-offs	$ (16,105)	(13,478)	(6,428)
Recoveries	12,253	9,564	2,433
Net (charge-offs) recoveries	(3,852)	(3,914)	(3,995)
Provision for loan losses	85,350	7,050	6,810
Ending balance	176,144	52,162	49,026
Individually evaluated	14,190	2,012	1,514
Collectively evaluated	161,954	48,179	44,960
Loans:
Individually evaluated	44,350	51,179
Collectively evaluated	10,889,297	9,466,195
Gross loans	10,933,647	9,689,638
Nonaccruing loans with no allowance for credit losses	8,977
Provision for other credit losses	1,500	0	0
Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Beginning balance	1,971	2,552
Ending balance		1,971	2,552
Loans:
Gross loans		172,264
Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	10,658	8,269	5,542
Charge-offs	(3,577)	(2,681)	(2,415)
Recoveries	1,263	1,428	618
Net (charge-offs) recoveries	(2,314)	(1,253)	(1,797)
Provision for loan losses	19,336	3,642	4,524
Ending balance	39,031	10,658	8,269
Individually evaluated	10,345	1,434	336
Collectively evaluated	28,686	8,932	7,772
Loans:
Individually evaluated	16,091	8,460
Collectively evaluated	2,520,893	1,329,974
Gross loans	2,536,984	1,367,972
Nonaccruing loans with no allowance for credit losses	541
Commercial, financial, agricultural | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Beginning balance	292	161
Ending balance		292	161
Loans:
Gross loans		29,538
Real estate - construction
Allowance for loan losses:
Beginning balance	5,029	4,755	3,428
Charge-offs	(716)	0	(51)
Recoveries	31	21	13
Net (charge-offs) recoveries	(685)	21	(38)
Provision for loan losses	8,198	253	1,365
Ending balance	16,047	5,029	4,755
Individually evaluated	497	16	68
Collectively evaluated	15,550	5,013	4,687
Loans:
Individually evaluated	497	12,416
Collectively evaluated	857,607	813,204
Gross loans	858,104	826,483
Nonaccruing loans with no allowance for credit losses	0
Real estate - construction | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Beginning balance	0	0
Ending balance		0	0
Loans:
Gross loans		863
Real estate - 1-4 family mortgage
Allowance for loan losses:
Beginning balance	9,814	10,139	12,009
Charge-offs	(1,167)	(1,602)	(2,023)
Recoveries	838	712	573
Net (charge-offs) recoveries	(329)	(890)	(1,450)
Provision for loan losses	8,366	565	(420)
Ending balance	32,165	9,814	10,139
Individually evaluated	300	160	79
Collectively evaluated	31,865	9,363	9,572
Loans:
Individually evaluated	5,379	20,262
Collectively evaluated	2,692,929	2,810,808
Gross loans	2,698,308	2,866,613
Nonaccruing loans with no allowance for credit losses	4,054
Real estate - 1-4 family mortgage | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Beginning balance	291	488
Ending balance		291	488
Loans:
Gross loans		35,543
Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	24,990	24,492	23,384
Charge-offs	(2,642)	(1,490)	(1,197)
Recoveries	2,478	689	1,108
Net (charge-offs) recoveries	(164)	(801)	(89)
Provision for loan losses	47,008	1,299	1,197
Ending balance	76,127	24,990	24,492
Individually evaluated	2,444	396	1,027
Collectively evaluated	73,683	23,208	21,564
Loans:
Individually evaluated	21,764	9,550
Collectively evaluated	4,533,088	4,131,582
Gross loans	4,554,852	4,244,265
Nonaccruing loans with no allowance for credit losses	4,382
Real estate – commercial mortgage: | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Beginning balance	1,386	1,901
Ending balance		1,386	1,901
Loans:
Gross loans		103,133
Lease financing
Allowance for loan losses:
Beginning balance	910
Charge-offs	(168)
Recoveries	11
Net (charge-offs) recoveries	(157)
Provision for loan losses	350
Ending balance	1,624	910
Individually evaluated	0
Collectively evaluated	1,624
Loans:
Individually evaluated	0
Collectively evaluated	75,862
Gross loans	75,862
Nonaccruing loans with no allowance for credit losses	0
Installment and Other
Allowance for loan losses:
Beginning balance	1,671	1,371	1,848
Charge-offs		(7,705)	(742)
Recoveries		6,714	121
Net (charge-offs) recoveries		(991)	(621)
Provision for loan losses		1,291	144
Ending balance		1,671	1,371
Individually evaluated		6	4
Collectively evaluated		1,663	1,365
Installment and Other | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Beginning balance	2	2
Ending balance		2	$ 2
Installment loans to individuals
Allowance for loan losses:
Beginning balance	761
Charge-offs	(7,835)
Recoveries	7,632
Net (charge-offs) recoveries	(203)
Provision for loan losses	2,092
Ending balance	11,150	761
Individually evaluated	604
Collectively evaluated	10,546
Loans:
Individually evaluated	619	491
Collectively evaluated	208,918	380,627
Gross loans	209,537	384,305
Nonaccruing loans with no allowance for credit losses	0
Installment loans to individuals | Receivables Acquired with Deteriorated Credit Quality
Loans:
Gross loans		3,187
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses:
Beginning balance	42,484
Ending balance		42,484
Cumulative Effect, Period of Adoption, Adjustment | Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	11,351
Ending balance		11,351
Cumulative Effect, Period of Adoption, Adjustment | Real estate - construction
Allowance for loan losses:
Beginning balance	3,505
Ending balance		3,505
Cumulative Effect, Period of Adoption, Adjustment | Real estate - 1-4 family mortgage
Allowance for loan losses:
Beginning balance	14,314
Ending balance		14,314
Cumulative Effect, Period of Adoption, Adjustment | Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	4,293
Ending balance		4,293
Cumulative Effect, Period of Adoption, Adjustment | Lease financing
Allowance for loan losses:
Beginning balance	521
Ending balance		521
Cumulative Effect, Period of Adoption, Adjustment | Installment loans to individuals
Allowance for loan losses:
Beginning balance	$ 8,500
Ending balance		$ 8,500