Loans and the Allowance for Loan Losses - (Details 6) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Loan portfolio by risk-rating grades
Total	$ 2,999,634	$ 2,092,260
Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	472,167	344,704
Lease financing
Loan portfolio by risk-rating grades
Total	419	0
Real estate – construction
Loan portfolio by risk-rating grades
Total	257,786	151,538
Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	275,480	140,166
Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	1,993,755	1,454,450
Installment loans to individuals
Loan portfolio by risk-rating grades
Total	27	1,402
Pass
Loan portfolio by risk-rating grades
Total	2,893,895	2,002,478
Pass | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	460,425	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	256,056	150,683
Pass | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	250,296	122,608
Pass | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	1,927,091	1,389,787
Pass | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	27	1,402
Watch
Loan portfolio by risk-rating grades
Total	60,822	43,298
Watch | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	7,583	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	1,692	855
Watch | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	10,736	6,079
Watch | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	40,811	31,109
Watch | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	0	0
Substandard
Loan portfolio by risk-rating grades
Total	44,917	46,484
Substandard | Commercial, financial, agricultural
Loan portfolio by risk-rating grades
Total	4,159	1,451
Substandard | Lease financing
Loan portfolio by risk-rating grades
Total	419	0
Substandard | Real estate – construction
Loan portfolio by risk-rating grades
Total	38	0
Substandard | Real estate – 1-4 family mortgage
Loan portfolio by risk-rating grades
Total	14,448	11,479
Substandard | Real estate – commercial mortgage
Loan portfolio by risk-rating grades
Total	25,853	33,554
Substandard | Installment loans to individuals
Loan portfolio by risk-rating grades
Total	$ 0	$ 0