Non Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Past due and nonaccrual loans
Total loans, gross	$ 7,451,394	$ 6,205,118
Unearned income	(2,786)	(2,409)
Loans, net of unearned income	7,448,608	6,202,709
Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	1,008,935	717,490
Loans, net of unearned income	1,008,935	717,490
Lease financing
Past due and nonaccrual loans
Total loans, gross	54,688	49,250
Real estate – construction
Past due and nonaccrual loans
Total loans, gross	577,720	552,679
Loans, net of unearned income	577,720	552,679
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	2,295,852	1,878,177
Loans, net of unearned income	2,295,852	1,878,177
Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	3,390,389	2,898,895
Loans, net of unearned income	3,390,389	2,898,895
Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	123,810	108,627
Loans, net of unearned income	175,712	155,468
Non purchased loans and leases
Past due and nonaccrual loans
Total loans, gross	5,296,253	4,715,981
Unearned income	(2,786)	(2,409)
Loans, net of unearned income	5,293,467	4,713,572
Non purchased loans and leases | Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	707,835	589,290
Non purchased loans and leases | Lease financing
Past due and nonaccrual loans
Total loans, gross	54,688	49,250
Non purchased loans and leases | Real estate – construction
Past due and nonaccrual loans
Total loans, gross	477,638	483,926
Non purchased loans and leases | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	1,644,060	1,425,730
Non purchased loans and leases | Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	2,311,340	2,075,137
Non purchased loans and leases | Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	100,692	92,648
Non purchased loans and leases | Accruing Loans
Past due and nonaccrual loans
Current Loans	5,267,810	4,689,425
Unearned income	(2,786)	(2,409)
Loans, net of unearned income	5,283,497	4,702,299
Non purchased loans and leases | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans	703,574	586,730
Total loans, gross	706,156	588,261
Non purchased loans and leases | Accruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans	54,047	48,919
Total loans, gross	54,523	49,112
Non purchased loans and leases | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans	477,235	482,931
Total loans, gross	477,638	483,926
Non purchased loans and leases | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans	1,632,983	1,414,254
Total loans, gross	1,640,274	1,421,579
Non purchased loans and leases | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans	2,302,423	2,066,821
Total loans, gross	2,307,068	2,069,203
Non purchased loans and leases | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans	100,334	92,179
Total loans, gross	100,624	92,627
Non purchased loans and leases | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	5,504	5,441
Unearned income	0	0
Loans, net of unearned income	9,970	11,273
Non purchased loans and leases | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans	278	97
Total loans, gross	1,679	1,029
Non purchased loans and leases | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	165	138
Non purchased loans and leases | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	0	0
Non purchased loans and leases | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans	2,234	2,768
Total loans, gross	3,786	4,151
Non purchased loans and leases | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans	2,969	2,576
Total loans, gross	4,272	5,934
Non purchased loans and leases | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans	23	0
Total loans, gross	68	21
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due	12,392	10,795
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	1,808	811
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	476	193
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	403	995
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	6,307	6,189
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	3,140	2,283
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	258	324
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due	748	741
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	538	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	210	161
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	0	580
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due	3,295	2,079
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	774	720
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	984	1,136
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	1,505	99
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	32	124
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due	3,718	5,091
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	863	932
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	165	138
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	1,342	1,222
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	1,303	2,778
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	$ 45	$ 21