Non 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
Non-Purchased
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	6,392,839	5,591,897
Unearned income	(3,127)	(3,341)
Loans, net of unearned income	6,389,712	5,588,556
Non-Purchased | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	6,359,292	5,558,312
Unearned income	(3,127)	(3,341)
Loans, net of unearned income	6,379,494	5,578,306
Non-Purchased | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	17,517	16,979
Non-Purchased | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	2,685	3,015
Non-Purchased | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,814	4,129
Unearned income	0	0
Loans, net of unearned income	10,218	10,250
Non-Purchased | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	241	206
Non-Purchased | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	7,163	5,915
Non-Purchased | Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	875,649	763,823
Non-Purchased | Commercial, financial, agricultural | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	870,457	759,143
Total loans, gross	874,121	761,887
Non-Purchased | Commercial, financial, agricultural | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	3,397	2,722
Non-Purchased | Commercial, financial, agricultural | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	267	22
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	172	698
Total loans, gross	1,528	1,936
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	0	205
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,356	1,033
Non-Purchased | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	64,992	57,354
Non-Purchased | Lease financing | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	64,296	57,148
Total loans, gross	64,992	57,195
Non-Purchased | Lease financing | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	607	47
Non-Purchased | Lease financing | Accruing Loans | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	89	0
Non-Purchased | Lease financing | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	0
Total loans, gross	0	159
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	0	159
Non-Purchased | Real estate – construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	635,519	547,658
Non-Purchased | Real estate – construction | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	634,632	547,608
Total loans, gross	635,519	547,658
Non-Purchased | Real estate – construction | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	887	50
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	2,087,890	1,729,534
Non-Purchased | Real estate – 1-4 family mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,071,401	1,712,982
Total loans, gross	2,083,930	1,726,986
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	10,378	11,810
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	2,151	2,194
Non-Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,046	730
Total loans, gross	3,960	2,548
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	238	0
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	2,676	1,818
Non-Purchased | Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	2,628,365	2,390,076
Non-Purchased | Real estate – commercial mortgage | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	2,621,902	2,381,871
Total loans, gross	2,623,795	2,384,519
Non-Purchased | Real estate – commercial mortgage | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	1,880	1,921
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	13	727
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	1,596	2,680
Total loans, gross	4,570	5,557
Non-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
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	2,974	2,877
Non-Purchased | Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	100,424	103,452
Non-Purchased | Installment loans to individuals | Accruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	99,731	102,901
Total loans, gross	100,264	103,402
Non-Purchased | Installment loans to individuals | Accruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	368	429
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	165	72
Non-Purchased | Installment loans to individuals | Nonaccruing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current Loans	0	21
Total loans, gross	160	50
Non-Purchased | Installment loans to individuals | Nonaccruing Loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans past due	3	1
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	$ 157	$ 28