Loans and Allowance for Loan Losses - Summary of Troubled Debt Restructuring by Loan Class, Defaulted under Restructured Terms (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014 Contract	Dec. 31, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of contracts	14	10
Troubled debt restructuring loans	$ 1,214	$ 3,390
Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	3
Troubled debt restructuring loans	236	525
Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	33	29
Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	3
Troubled debt restructuring loans	570	2,197
Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	3
Troubled debt restructuring loans	314	639
Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4
Troubled debt restructuring loans	$ 61