Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	$ 9,693,463	$ 9,086,256
Unearned income	(3,825)	(3,127)
Loans, net of unearned income	9,689,638	9,083,129
Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,367,972	1,295,912
Loans, net of unearned income	1,367,972	1,295,912
Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	85,700	64,992
Real estate – construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	826,483	740,668
Loans, net of unearned income	826,483	740,668
Real estate – 1-4 family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	2,866,613	2,795,343
Loans, net of unearned income	2,866,613	2,795,343
Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	4,244,265	4,051,509
Loans, net of unearned income	4,244,265	4,051,509
Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	302,430	137,832
Loans, net of unearned income	384,305	199,697
Purchased
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	2,101,664	2,693,417
Unearned income	0	0
Loans, net of unearned income	2,101,664	2,693,417
Purchased | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,075,422	2,661,269
Unearned income	0	0
Loans, net of unearned income	2,094,626	2,687,581
Purchased | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	14,887	19,080
Unearned income	0	0
Purchased | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	4,317	7,232
Unearned income	0	0
Purchased | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,250	1,849
Unearned income	0	0
Loans, net of unearned income	7,038	5,836
Purchased | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	606	204
Unearned income	0	0
Purchased | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	4,182	3,783
Unearned income	0	0
Purchased | Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	315,619	420,263
Purchased | Commercial, financial, agricultural | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	311,218	417,786
Total loans, gross	314,105	419,694
Purchased | Commercial, financial, agricultural | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,889	1,811
Purchased | Commercial, financial, agricultural | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	998	97
Purchased | Commercial, financial, agricultural | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	268	92
Total loans, gross	1,514	569
Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,246	477
Purchased | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	0	0
Purchased | Lease financing | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	0
Total loans, gross	0	0
Purchased | Lease financing | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Lease financing | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Lease financing | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	0
Total loans, gross	0	0
Purchased | Lease financing | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Lease financing | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Real estate – construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	51,582	105,149
Purchased | Real estate – construction | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	51,263	103,846
Total loans, gross	51,582	105,149
Purchased | Real estate – construction | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	319	1,235
Purchased | Real estate – construction | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	68
Purchased | Real estate – construction | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	0
Total loans, gross	0	0
Purchased | Real estate – construction | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Real estate – construction | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Real estate – 1-4 family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	516,487	707,453
Purchased | Real estate – 1-4 family mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	503,826	690,697
Total loans, gross	511,586	704,133
Purchased | Real estate – 1-4 family mortgage | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	5,516	8,981
Purchased | Real estate – 1-4 family mortgage | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	2,244	4,455
Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,534	1,237
Total loans, gross	4,901	3,320
Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	605	202
Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	2,762	1,881
Purchased | Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,115,389	1,423,144
Purchased | Real estate – commercial mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,110,570	1,413,346
Total loans, gross	1,114,946	1,421,467
Purchased | Real estate – commercial mortgage | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	3,454	5,711
Purchased | Real estate – commercial mortgage | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	922	2,410
Purchased | Real estate – commercial mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	320	276
Total loans, gross	443	1,677
Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	123	1,401
Purchased | Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	102,587	37,408
Purchased | Installment loans to individuals | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	98,545	35,594
Total loans, gross	102,407	37,138
Purchased | Installment loans to individuals | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	3,709	1,342
Purchased | Installment loans to individuals | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	153	202
Purchased | Installment loans to individuals | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	128	244
Total loans, gross	180	270
Purchased | Installment loans to individuals | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1	2
Purchased | Installment loans to individuals | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	$ 51	$ 24