Loans - Schedule of Accounts Notes Loans and Financial Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	$ 1,999,420	$ 1,889,881	$ 1,695,382
Commercial, Financial & Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	334,917	319,654	270,571
Real Estate - Construction & Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	178,568	161,507	149,543
Commercial And Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	947,274	907,524	836,230
Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	496,043	456,106	393,001
Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	29,113	30,782	32,345
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and deferred loan fees receivables	$ 13,505	$ 14,308	$ 13,692