Non 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
Non-Purchased
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	7,591,799	6,392,839
Unearned income	(3,825)	(3,127)
Loans, net of unearned income	7,587,974	6,389,712
Non-Purchased | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	7,540,226	6,359,292
Unearned income	(3,825)	(3,127)
Loans, net of unearned income	7,566,465	6,379,494
Non-Purchased | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	22,781	17,517
Unearned income	0	0
Non-Purchased | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	3,458	2,685
Unearned income	0	0
Non-Purchased | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	3,635	2,814
Unearned income	0	0
Loans, net of unearned income	21,509	10,218
Non-Purchased | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,382	241
Unearned income	0	0
Non-Purchased | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	16,492	7,163
Unearned income	0	0
Non-Purchased | Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,052,353	875,649
Non-Purchased | Commercial, financial, agricultural | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,045,802	870,457
Total loans, gross	1,046,883	874,121
Non-Purchased | Commercial, financial, agricultural | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	605	3,397
Non-Purchased | Commercial, financial, agricultural | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	476	267
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	60	172
Total loans, gross	5,470	1,528
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	387	0
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	5,023	1,356
Non-Purchased | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	85,700	64,992
Non-Purchased | Lease financing | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	85,474	64,296
Total loans, gross	85,474	64,992
Non-Purchased | Lease financing | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	607
Non-Purchased | Lease financing | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	89
Non-Purchased | Lease financing | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	0
Total loans, gross	226	0
Non-Purchased | Lease financing | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Non-Purchased | Lease financing | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	226	0
Non-Purchased | Real estate – construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	774,901	635,519
Non-Purchased | Real estate – construction | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	774,107	634,632
Total loans, gross	774,901	635,519
Non-Purchased | Real estate – construction | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	794	887
Non-Purchased | Real estate – construction | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Non-Purchased | Real estate – construction | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	0
Total loans, gross	0	0
Non-Purchased | Real estate – construction | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	0
Non-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
Non-Purchased | Real estate – 1-4 family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	2,350,126	2,087,890
Non-Purchased | Real estate – 1-4 family mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,320,328	2,071,401
Total loans, gross	2,340,850	2,083,930
Non-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	18,020	10,378
Non-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	2,502	2,151
Non-Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,082	1,046
Total loans, gross	9,276	3,960
Non-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	623	238
Non-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	6,571	2,676
Non-Purchased | Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	3,128,876	2,628,365
Non-Purchased | Real estate – commercial mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	3,119,785	2,621,902
Total loans, gross	3,122,423	2,623,795
Non-Purchased | Real estate – commercial mortgage | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	2,362	1,880
Non-Purchased | Real estate – commercial mortgage | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	276	13
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,426	1,596
Total loans, gross	6,453	4,570
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	372	0
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	4,655	2,974
Non-Purchased | Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	199,843	100,424
Non-Purchased | Installment loans to individuals | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	198,555	99,731
Total loans, gross	199,759	100,264
Non-Purchased | Installment loans to individuals | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,000	368
Non-Purchased | Installment loans to individuals | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	204	165
Non-Purchased | Installment loans to individuals | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	67	0
Total loans, gross	84	160
Non-Purchased | Installment loans to individuals | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	3
Non-Purchased | Installment loans to individuals | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	$ 17	$ 157