Non Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Loan portfolio not subject to risk rating
Total	$ 7,698,070	$ 7,620,322
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,046,818	1,039,393
Real estate – construction
Loan portfolio not subject to risk rating
Total	657,491	633,389
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,358,101	2,343,721
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	3,463,953	3,427,530
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	171,707	176,289
Non purchased loans and leases
Loan portfolio not subject to risk rating
Total	5,830,122	5,588,556
Non purchased loans and leases | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	2,267,958	2,210,289
Non purchased loans and leases | Performing and Nonperforming | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	200,158	192,982
Non purchased loans and leases | Performing and Nonperforming | Lease financing
Loan portfolio not subject to risk rating
Total	52,536	54,013
Non purchased loans and leases | Performing and Nonperforming | Real estate – construction
Loan portfolio not subject to risk rating
Total	60,697	63,417
Non purchased loans and leases | Performing and Nonperforming | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	1,514,886	1,465,689
Non purchased loans and leases | Performing and Nonperforming | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	337,474	331,657
Non purchased loans and leases | Performing and Nonperforming | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	102,207	102,531
Non purchased loans and leases | Performing
Loan portfolio not subject to risk rating
Total	2,260,912	2,203,941
Non purchased loans and leases | Performing | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	198,111	191,473
Non purchased loans and leases | Performing | Lease financing
Loan portfolio not subject to risk rating
Total	52,334	53,854
Non purchased loans and leases | Performing | Real estate – construction
Loan portfolio not subject to risk rating
Total	60,648	63,417
Non purchased loans and leases | Performing | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	1,511,105	1,462,347
Non purchased loans and leases | Performing | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	336,584	330,441
Non purchased loans and leases | Performing | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	102,130	102,409
Non purchased loans and leases | Non- Performing
Loan portfolio not subject to risk rating
Total	7,046	6,348
Non purchased loans and leases | Non- Performing | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	2,047	1,509
Non purchased loans and leases | Non- Performing | Lease financing
Loan portfolio not subject to risk rating
Total	202	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	3,781	3,342
Non purchased loans and leases | Non- Performing | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	890	1,216
Non purchased loans and leases | Non- Performing | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	$ 77	$ 122