Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Past due and nonaccrual loans
Loans, net of unearned income	$ 11,084,738	$ 9,689,638
Commercial, financial, agricultural
Past due and nonaccrual loans
Loans, net of unearned income	2,648,062	1,367,972
Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	773,119	826,483
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	2,760,394	2,866,613
Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	4,577,009	4,244,265
Installment loans to individuals
Past due and nonaccrual loans
Loans, net of unearned income	243,226	384,305
Purchased loans
Past due and nonaccrual loans
Loans, net of unearned income	1,660,514	2,101,664
Purchased loans | Accruing loans
Past due and nonaccrual loans
Loans, net of unearned income	1,635,693	2,094,626
Current Loans	1,628,985	2,075,422
Purchased loans | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	6,390	14,887
Purchased loans | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	318	4,317
Purchased loans | Nonaccruing loans
Past due and nonaccrual loans
Loans, net of unearned income	24,821	7,038
Current Loans	10,037	2,250
Purchased loans | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	2,642	606
Purchased loans | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	12,142	4,182
Purchased loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans, net of unearned income	202,768	315,619
Purchased loans | Commercial, financial, agricultural | Accruing loans
Past due and nonaccrual loans
Current, gross	189,668	311,218
Loans, net of unearned income	190,760	314,105
Purchased loans | Commercial, financial, agricultural | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	1,056	1,889
Purchased loans | Commercial, financial, agricultural | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	36	998
Purchased loans | Commercial, financial, agricultural | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	4,120	268
Loans, net of unearned income	12,008	1,514
Purchased loans | Commercial, financial, agricultural | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	1,655	0
Purchased loans | Commercial, financial, agricultural | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	6,233	1,246
Purchased loans | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	34,246	51,582
Purchased loans | Real estate – construction: | Accruing loans
Past due and nonaccrual loans
Current, gross	34,246	51,263
Loans, net of unearned income	34,246	51,582
Purchased loans | Real estate – construction: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0	319
Purchased loans | Real estate – construction: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0	0
Purchased loans | Real estate – construction: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	0	0
Loans, net of unearned income	0	0
Purchased loans | Real estate – construction: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0	0
Purchased loans | Real estate – construction: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0	0
Purchased loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	391,102	516,487
Purchased loans | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	380,933	503,826
Loans, net of unearned income	383,151	511,586
Purchased loans | Real estate – 1-4 family mortgage | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	2,040	5,516
Purchased loans | Real estate – 1-4 family mortgage | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	178	2,244
Purchased loans | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	3,462	1,534
Loans, net of unearned income	7,951	4,901
Purchased loans | Real estate – 1-4 family mortgage | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	329	605
Purchased loans | Real estate – 1-4 family mortgage | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	4,160	2,762
Purchased loans | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	966,367	1,115,389
Purchased loans | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	960,292	1,110,570
Loans, net of unearned income	961,796	1,114,946
Purchased loans | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	1,450	3,454
Purchased loans | Real estate – commercial mortgage: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	54	922
Purchased loans | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	2,296	320
Loans, net of unearned income	4,571	443
Purchased loans | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	649	0
Purchased loans | Real estate – commercial mortgage: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	1,626	123
Purchased loans | Installment loans to individuals
Past due and nonaccrual loans
Loans, net of unearned income	66,031	102,587
Purchased loans | Installment loans to individuals | Accruing loans
Past due and nonaccrual loans
Current, gross	63,846	98,545
Loans, net of unearned income	65,740	102,407
Purchased loans | Installment loans to individuals | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	1,844	3,709
Purchased loans | Installment loans to individuals | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	50	153
Purchased loans | Installment loans to individuals | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	159	128
Loans, net of unearned income	291	180
Purchased loans | Installment loans to individuals | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	9	1
Purchased loans | Installment loans to individuals | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	123	51
Purchased loans | Residential | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	3,093	16,407
Purchased loans | Residential | Real estate – construction: | Accruing loans
Past due and nonaccrual loans
Current, gross	3,093
Loans, net of unearned income	3,093
Purchased loans | Residential | Real estate – construction: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Residential | Real estate – construction: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Residential | Real estate – construction: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	0
Loans, net of unearned income	0
Purchased loans | Residential | Real estate – construction: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Residential | Real estate – construction: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Commercial | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	31,153	35,175
Purchased loans | Commercial | Real estate – construction: | Accruing loans
Past due and nonaccrual loans
Current, gross	31,153
Loans, net of unearned income	31,153
Purchased loans | Commercial | Real estate – construction: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Commercial | Real estate – construction: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Commercial | Real estate – construction: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	0
Loans, net of unearned income	0
Purchased loans | Commercial | Real estate – construction: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Commercial | Real estate – construction: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Primary | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	245,369	332,729
Purchased loans | Primary | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	238,937
Loans, net of unearned income	239,846
Purchased loans | Primary | Real estate – 1-4 family mortgage | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	845
Purchased loans | Primary | Real estate – 1-4 family mortgage | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	64
Purchased loans | Primary | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	2,400
Loans, net of unearned income	5,523
Purchased loans | Primary | Real estate – 1-4 family mortgage | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	329
Purchased loans | Primary | Real estate – 1-4 family mortgage | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	2,794
Purchased loans | Home equity | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	95,235	117,275
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	93,006
Loans, net of unearned income	93,959
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	839
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	114
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	647
Loans, net of unearned income	1,276
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	629
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	33,567	43,169
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	32,409
Loans, net of unearned income	32,765
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	356
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	94
Loans, net of unearned income	802
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	708
Purchased loans | Land development | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	16,931	23,314
Purchased loans | Land development | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	16,581
Loans, net of unearned income	16,581
Purchased loans | Land development | Real estate – 1-4 family mortgage | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Land development | Real estate – 1-4 family mortgage | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Land development | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	321
Loans, net of unearned income	350
Purchased loans | Land development | Real estate – 1-4 family mortgage | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Land development | Real estate – 1-4 family mortgage | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	29
Purchased loans | Land development | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	32,694
Purchased loans | Land development | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	32,142
Loans, net of unearned income	32,303
Purchased loans | Land development | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	161
Purchased loans | Land development | Real estate – commercial mortgage: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Land development | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	227
Loans, net of unearned income	391
Purchased loans | Land development | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Land development | Real estate – commercial mortgage: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	164
Purchased loans | Owner-occupied | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	355,994	428,077
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	351,688
Loans, net of unearned income	352,539
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	851
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	0
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	2,059
Loans, net of unearned income	3,455
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	505
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	891
Purchased loans | Non-owner occupied | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	577,679	$ 647,308
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	576,462
Loans, net of unearned income	576,954
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	438
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	54
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	10
Loans, net of unearned income	725
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	144
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	$ 571