Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	$ 9,086,256	$ 7,623,663
Unearned income	(3,127)	(3,341)
Loans, net of unearned income	9,083,129	7,620,322
Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,295,912	1,039,393
Loans, net of unearned income	1,295,912	1,039,393
Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	64,992	57,354
Real estate – construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	740,668	633,389
Loans, net of unearned income	740,668	633,389
Real estate – 1-4 family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	2,795,343	2,343,721
Loans, net of unearned income	2,795,343	2,343,721
Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	4,051,509	3,427,530
Loans, net of unearned income	4,051,509	3,427,530
Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	137,832	122,276
Loans, net of unearned income	199,697	176,289
Purchased
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	2,693,417	2,031,766
Unearned income	0	0
Loans, net of unearned income	2,693,417	2,031,766
Purchased | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,661,269	2,010,852
Unearned income	0	0
Loans, net of unearned income	2,687,581	2,027,342
Purchased | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	19,080	10,759
Purchased | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	7,232	5,731
Purchased | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,849	2,612
Unearned income	0	0
Loans, net of unearned income	5,836	4,424
Purchased | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	204	635
Purchased | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	3,783	1,177
Purchased | Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	420,263	275,570
Purchased | Commercial, financial, agricultural | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	417,786	273,488
Total loans, gross	419,694	275,139
Purchased | Commercial, financial, agricultural | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,811	1,119
Purchased | Commercial, financial, agricultural | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	97	532
Purchased | Commercial, financial, agricultural | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	92	232
Total loans, gross	569	431
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	477	199
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	105,149	85,731
Purchased | Real estate – construction | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	103,846	85,316
Total loans, gross	105,149	85,731
Purchased | Real estate – construction | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,235	415
Purchased | Real estate – construction | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	68	0
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	707,453	614,187
Purchased | Real estate – 1-4 family mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	690,697	602,464
Total loans, gross	704,133	610,814
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	8,981	6,070
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	4,455	2,280
Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,237	2,109
Total loans, gross	3,320	3,373
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	202	385
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	1,881	879
Purchased | Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,423,144	1,037,454
Purchased | Real estate – commercial mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,413,346	1,031,141
Total loans, gross	1,421,467	1,036,998
Purchased | Real estate – commercial mortgage | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	5,711	2,947
Purchased | Real estate – commercial mortgage | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	2,410	2,910
Purchased | Real estate – commercial mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	276	166
Total loans, gross	1,677	456
Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	191
Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,401	99
Purchased | Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	37,408	18,824
Purchased | Installment loans to individuals | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	35,594	18,443
Total loans, gross	37,138	18,660
Purchased | Installment loans to individuals | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,342	208
Purchased | Installment loans to individuals | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	202	9
Purchased | Installment loans to individuals | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	244	105
Total loans, gross	270	164
Purchased | Installment loans to individuals | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	2	59
Purchased | Installment loans to individuals | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	$ 24	$ 0