Loans and the Allowance for Loan Losses - (Details 6) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Loan portfolio by risk-rating grades
Total	$ 2,101,701	$ 2,092,260
Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	330,691	344,704
Lease financing
Loan portfolio by risk-rating grades
Total	415	0
Real estate – construction
Loan portfolio by risk-rating grades
Total	148,796	151,538
Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	142,521	140,166
Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	1,479,269	1,454,450
Installment loans to individuals
Loan portfolio by risk-rating grades
Total	9	1,402
Pass
Loan portfolio by risk-rating grades
Total	2,030,873	2,002,478
Pass | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	325,883	337,998
Pass | Lease financing
Loan portfolio by risk-rating grades
Total	0	0
Pass | Real estate – construction
Loan portfolio by risk-rating grades
Total	148,161	150,683
Pass | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	126,332	122,608
Pass | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	1,430,488	1,389,787
Pass | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	9	1,402
Watch
Loan portfolio by risk-rating grades
Total	33,747	43,298
Watch | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	3,686	5,255
Watch | Lease financing
Loan portfolio by risk-rating grades
Total	0	0
Watch | Real estate – construction
Loan portfolio by risk-rating grades
Total	635	855
Watch | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	4,079	6,079
Watch | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	25,347	31,109
Watch | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	0	0
Substandard
Loan portfolio by risk-rating grades
Total	37,081	46,484
Substandard | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	1,122	1,451
Substandard | Lease financing
Loan portfolio by risk-rating grades
Total	415	0
Substandard | Real estate – construction
Loan portfolio by risk-rating grades
Total	0	0
Substandard | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	12,110	11,479
Substandard | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	23,434	33,554
Substandard | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	$ 0	$ 0