Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Past due and nonaccrual loans
Loans, net of unearned income	$ 11,000,796	$ 9,693,463
Commercial, financial, agricultural
Past due and nonaccrual loans
Loans, net of unearned income	2,641,598	1,367,972
Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	791,108	826,483
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	2,788,513	2,866,613
Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	4,410,753	4,244,265
Installment loans to individuals
Past due and nonaccrual loans
Loans, net of unearned income	284,553	302,430
Residential | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	295,931	289,050
Commercial | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	495,177	537,433
Primary | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	1,756,253	1,781,948
Home equity | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	543,468	573,540
Rental/investment | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	318,803	335,100
Land development | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	169,989	176,025
Land development | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	155,766	156,089
Owner-occupied | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	1,660,674	1,637,281
Non-owner occupied | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	2,594,313	2,450,895
Purchased loans
Past due and nonaccrual loans
Loans, net of unearned income	1,791,203	2,101,664
Purchased loans | Accruing loans
Past due and nonaccrual loans
Loans, net of unearned income	1,769,842	2,094,626
Current Loans	1,764,595	2,075,422
Purchased loans | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	3,089	14,887
Purchased loans | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	2,158	4,317
Purchased loans | Nonaccruing loans
Past due and nonaccrual loans
Loans, net of unearned income	21,361	7,038
Current Loans	10,084	2,250
Purchased loans | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	1,826	606
Purchased loans | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	9,451	4,182
Purchased loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans, net of unearned income	225,355	315,619
Purchased loans | Commercial, financial, agricultural | Accruing loans
Past due and nonaccrual loans
Current, gross	218,892	311,218
Loans, net of unearned income	219,241	314,105
Purchased loans | Commercial, financial, agricultural | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	161	1,889
Purchased loans | Commercial, financial, agricultural | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	188	998
Purchased loans | Commercial, financial, agricultural | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	4,670	268
Loans, net of unearned income	6,114	1,514
Purchased loans | Commercial, financial, agricultural | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	0	0
Purchased loans | Commercial, financial, agricultural | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	1,444	1,246
Purchased loans | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	34,236	51,582
Purchased loans | Real estate – construction: | Accruing loans
Past due and nonaccrual loans
Current, gross	34,236	51,263
Loans, net of unearned income	34,236	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	445,526	516,487
Purchased loans | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	434,457	503,826
Loans, net of unearned income	436,356	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	901	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	998	2,244
Purchased loans | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	2,380	1,534
Loans, net of unearned income	9,170	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	1,712	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	5,078	2,762
Purchased loans | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	1,010,035	1,115,389
Purchased loans | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	1,002,822	1,110,570
Loans, net of unearned income	1,004,258	1,114,946
Purchased loans | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	532	3,454
Purchased loans | Real estate – commercial mortgage: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	904	922
Purchased loans | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	2,885	320
Loans, net of unearned income	5,777	443
Purchased loans | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	80	0
Purchased loans | Real estate – commercial mortgage: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	2,812	123
Purchased loans | Installment loans to individuals
Past due and nonaccrual loans
Loans, net of unearned income	76,051	102,587
Purchased loans | Installment loans to individuals | Accruing loans
Past due and nonaccrual loans
Current, gross	74,188	98,545
Loans, net of unearned income	75,751	102,407
Purchased loans | Installment loans to individuals | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	1,495	3,709
Purchased loans | Installment loans to individuals | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	68	153
Purchased loans | Installment loans to individuals | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	149	128
Loans, net of unearned income	300	180
Purchased loans | Installment loans to individuals | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	34	1
Purchased loans | Installment loans to individuals | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	117	51
Purchased loans | Residential | Real estate – construction:
Past due and nonaccrual loans
Loans, net of unearned income	3,948	16,407
Purchased loans | Residential | Real estate – construction: | Accruing loans
Past due and nonaccrual loans
Current, gross	3,948
Loans, net of unearned income	3,948
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	30,288	35,175
Purchased loans | Commercial | Real estate – construction: | Accruing loans
Past due and nonaccrual loans
Current, gross	30,288
Loans, net of unearned income	30,288
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	280,057	332,729
Purchased loans | Primary | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	272,048
Loans, net of unearned income	273,514
Purchased loans | Primary | Real estate – 1-4 family mortgage | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	654
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	812
Purchased loans | Primary | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	1,220
Loans, net of unearned income	6,543
Purchased loans | Primary | Real estate – 1-4 family mortgage | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	1,575
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	3,748
Purchased loans | Home equity | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	102,694	117,275
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	100,915
Loans, net of unearned income	101,293
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	224
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	154
Purchased loans | Home equity | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	788
Loans, net of unearned income	1,401
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	137
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	476
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	41,156	43,169
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	40,249
Loans, net of unearned income	40,304
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	23
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	32
Purchased loans | Rental/investment | Real estate – 1-4 family mortgage | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	128
Loans, net of unearned income	852
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	724
Purchased loans | Land development | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans, net of unearned income	21,619	23,314
Purchased loans | Land development | Real estate – 1-4 family mortgage | Accruing loans
Past due and nonaccrual loans
Current, gross	21,245
Loans, net of unearned income	21,245
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	244
Loans, net of unearned income	374
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	130
Purchased loans | Land development | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	36,989
Purchased loans | Land development | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	36,457
Loans, net of unearned income	36,507
Purchased loans | Land development | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	50
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	247
Loans, net of unearned income	482
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	235
Purchased loans | Owner-occupied | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	390,477	428,077
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	385,222
Loans, net of unearned income	386,035
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	427
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Accruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	386
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	2,492
Loans, net of unearned income	4,442
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	70
Purchased loans | Owner-occupied | Real estate – commercial mortgage: | Nonaccruing loans | 90 Days or More Past Due
Past due and nonaccrual loans
Past due, gross	1,880
Purchased loans | Non-owner occupied | Real estate – commercial mortgage:
Past due and nonaccrual loans
Loans, net of unearned income	582,569	$ 647,308
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Accruing loans
Past due and nonaccrual loans
Current, gross	581,143
Loans, net of unearned income	581,716
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Accruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	55
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	518
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Nonaccruing loans
Past due and nonaccrual loans
Current, gross	146
Loans, net of unearned income	853
Purchased loans | Non-owner occupied | Real estate – commercial mortgage: | Nonaccruing loans | 30-89 Days Past Due
Past due and nonaccrual loans
Past due, gross	10
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	$ 697