Non Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Loan portfolio not subject to risk rating
Total	$ 7,767,657	$ 7,620,322
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	987,818	1,039,393
Real estate – construction
Loan portfolio not subject to risk rating
Total	712,818	633,389
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,433,099	2,343,721
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	3,461,174	3,427,530
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	172,748	176,289
Non purchased loans and leases
Loan portfolio not subject to risk rating
Total	6,057,766	5,588,556
Non purchased loans and leases | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	2,368,618	2,210,289
Non purchased loans and leases | Performing and Nonperforming | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	196,180	192,982
Non purchased loans and leases | Performing and Nonperforming | Lease financing
Loan portfolio not subject to risk rating
Total	52,423	54,013
Non purchased loans and leases | Performing and Nonperforming | Real estate – construction
Loan portfolio not subject to risk rating
Total	58,992	63,417
Non purchased loans and leases | Performing and Nonperforming | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	1,622,340	1,465,689
Non purchased loans and leases | Performing and Nonperforming | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	334,036	331,657
Non purchased loans and leases | Performing and Nonperforming | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	104,647	102,531
Non purchased loans and leases | Performing
Loan portfolio not subject to risk rating
Total	2,362,349	2,203,941
Non purchased loans and leases | Performing | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	194,765	191,473
Non purchased loans and leases | Performing | Lease financing
Loan portfolio not subject to risk rating
Total	52,044	53,854
Non purchased loans and leases | Performing | Real estate – construction
Loan portfolio not subject to risk rating
Total	58,943	63,417
Non purchased loans and leases | Performing | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	1,618,669	1,462,347
Non purchased loans and leases | Performing | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	333,351	330,441
Non purchased loans and leases | Performing | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	104,577	102,409
Non purchased loans and leases | Non- Performing
Loan portfolio not subject to risk rating
Total	6,269	6,348
Non purchased loans and leases | Non- Performing | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,415	1,509
Non purchased loans and leases | Non- Performing | Lease financing
Loan portfolio not subject to risk rating
Total	379	159
Non purchased loans and leases | Non- Performing | Real estate – construction
Loan portfolio not subject to risk rating
Total	49	0
Non purchased loans and leases | Non- Performing | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	3,671	3,342
Non purchased loans and leases | Non- Performing | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	685	1,216
Non purchased loans and leases | Non- Performing | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	$ 70	$ 122