Non Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Past due and nonaccrual loans
Total loans, gross	$ 7,623,663	$ 6,205,118
Unearned income	(3,341)	(2,409)
Loans, net of unearned income	7,620,322	6,202,709
Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	1,039,393	717,490
Loans, net of unearned income	1,039,393	717,490
Lease financing
Past due and nonaccrual loans
Total loans, gross	57,354	49,250
Real estate – construction
Past due and nonaccrual loans
Total loans, gross	633,389	552,679
Loans, net of unearned income	633,389	552,679
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	2,343,721	1,878,177
Loans, net of unearned income	2,343,721	1,878,177
Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	3,427,530	2,898,895
Loans, net of unearned income	3,427,530	2,898,895
Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	122,276	108,627
Loans, net of unearned income	176,289	155,468
Non-Purchased
Past due and nonaccrual loans
Total loans, gross	5,591,897	4,715,981
Unearned income	(3,341)	(2,409)
Loans, net of unearned income	5,588,556	4,713,572
Non-Purchased | Accruing Loans
Past due and nonaccrual loans
Current Loans	5,558,312	4,689,425
Unearned income	(3,341)	(2,409)
Loans, net of unearned income	5,578,306	4,702,299
Non-Purchased | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	16,979	10,795
Non-Purchased | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	3,015	2,079
Non-Purchased | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	4,129	5,441
Unearned income	0	0
Loans, net of unearned income	10,250	11,273
Non-Purchased | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	206	741
Non-Purchased | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	5,915	5,091
Non-Purchased | Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	763,823	589,290
Non-Purchased | Commercial, financial, agricultural | Accruing Loans
Past due and nonaccrual loans
Current Loans	759,143	586,730
Total loans, gross	761,887	588,261
Non-Purchased | Commercial, financial, agricultural | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	2,722	811
Non-Purchased | Commercial, financial, agricultural | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	22	720
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	698	97
Total loans, gross	1,936	1,029
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	205	0
Non-Purchased | Commercial, financial, agricultural | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	1,033	932
Non-Purchased | Lease financing
Past due and nonaccrual loans
Total loans, gross	57,354	49,250
Non-Purchased | Lease financing | Accruing Loans
Past due and nonaccrual loans
Current Loans	57,148	48,919
Total loans, gross	57,195	49,112
Non-Purchased | Lease financing | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	47	193
Non-Purchased | Lease financing | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	0	0
Non-Purchased | Lease financing | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	159	138
Non-Purchased | Lease financing | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	0	0
Non-Purchased | Lease financing | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	159	138
Non-Purchased | Real estate – construction
Past due and nonaccrual loans
Total loans, gross	547,658	483,926
Non-Purchased | Real estate – construction | Accruing Loans
Past due and nonaccrual loans
Current Loans	547,608	482,931
Total loans, gross	547,658	483,926
Non-Purchased | Real estate – construction | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	50	995
Non-Purchased | Real estate – construction | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	0	0
Non-Purchased | Real estate – construction | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	0	0
Non-Purchased | Real estate – construction | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	0	0
Non-Purchased | Real estate – construction | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	0	0
Non-Purchased | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	1,729,534	1,425,730
Non-Purchased | Real estate – 1-4 family mortgage | Accruing Loans
Past due and nonaccrual loans
Current Loans	1,712,982	1,414,254
Total loans, gross	1,726,986	1,421,579
Non-Purchased | Real estate – 1-4 family mortgage | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	11,810	6,189
Non-Purchased | Real estate – 1-4 family mortgage | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	2,194	1,136
Non-Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	730	2,768
Total loans, gross	2,548	4,151
Non-Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	0	161
Non-Purchased | Real estate – 1-4 family mortgage | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	1,818	1,222
Non-Purchased | Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	2,390,076	2,075,137
Non-Purchased | Real estate – commercial mortgage | Accruing Loans
Past due and nonaccrual loans
Current Loans	2,381,871	2,066,821
Total loans, gross	2,384,519	2,069,203
Non-Purchased | Real estate – commercial mortgage | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	1,921	2,283
Non-Purchased | Real estate – commercial mortgage | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	727	99
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	2,680	2,576
Total loans, gross	5,557	5,934
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	0	580
Non-Purchased | Real estate – commercial mortgage | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	2,877	2,778
Non-Purchased | Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	103,452	92,648
Non-Purchased | Installment loans to individuals | Accruing Loans
Past due and nonaccrual loans
Current Loans	102,901	92,179
Total loans, gross	103,402	92,627
Non-Purchased | Installment loans to individuals | Accruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	429	324
Non-Purchased | Installment loans to individuals | Accruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	72	124
Non-Purchased | Installment loans to individuals | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	21	0
Total loans, gross	50	21
Non-Purchased | Installment loans to individuals | Nonaccruing Loans | 30-89 Days Past Due
Past due and nonaccrual loans
Loans past due	1	0
Non-Purchased | Installment loans to individuals | Nonaccruing Loans | 90 Days or More Past Due
Past due and nonaccrual loans
Loans past due	$ 28	$ 21