Non Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Loan portfolio not subject to risk rating
Total	$ 9,088,293	$ 9,083,129
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,308,457	1,295,912
Real estate – construction
Loan portfolio not subject to risk rating
Total	741,073	740,668
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,769,173	2,795,343
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	4,083,632	4,051,509
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	185,958	199,697
Non purchased loans and leases
Loan portfolio not subject to risk rating
Total	6,565,599	6,389,712
Non purchased loans and leases | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	2,568,113	2,560,335
Non purchased loans and leases | Performing and Nonperforming | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	218,918	234,547
Non purchased loans and leases | Performing and Nonperforming | Lease financing
Loan portfolio not subject to risk rating
Total	58,651	61,865
Non purchased loans and leases | Performing and Nonperforming | Real estate – construction
Loan portfolio not subject to risk rating
Total	66,856	66,551
Non purchased loans and leases | Performing and Nonperforming | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	1,786,989	1,757,406
Non purchased loans and leases | Performing and Nonperforming | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	343,045	339,542
Non purchased loans and leases | Performing and Nonperforming | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	93,654	100,424
Non purchased loans and leases | Performing
Loan portfolio not subject to risk rating
Total	2,561,082	2,551,833
Non purchased loans and leases | Performing | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	217,572	233,046
Non purchased loans and leases | Performing | Lease financing
Loan portfolio not subject to risk rating
Total	58,562	61,776
Non purchased loans and leases | Performing | Real estate – construction
Loan portfolio not subject to risk rating
Total	66,856	66,551
Non purchased loans and leases | Performing | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	1,782,390	1,751,994
Non purchased loans and leases | Performing | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	342,170	338,367
Non purchased loans and leases | Performing | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	93,532	100,099
Non purchased loans and leases | Non- Performing
Loan portfolio not subject to risk rating
Total	7,031	8,502
Non purchased loans and leases | Non- Performing | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,346	1,501
Non purchased loans and leases | Non- Performing | Lease financing
Loan portfolio not subject to risk rating
Total	89	89
Non purchased loans and leases | Non- Performing | Real estate – construction
Loan portfolio not subject to risk rating
Total	0	0
Non purchased loans and leases | Non- Performing | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	4,599	5,412
Non purchased loans and leases | Non- Performing | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	875	1,175
Non purchased loans and leases | Non- Performing | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	$ 122	$ 325