Loans - Summary of Troubled Debt Restructuring by Loan Class, Classified Separately Under Terms (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013 Contract	Dec. 31, 2012 Contract	Sep. 30, 2012 Contract
Loans Currently Paying Under Restructured Terms [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	56	54	50
Troubled debt restructuring loans	$ 16,258	$ 18,738	$ 19,893
Loans Currently Paying Under Restructured Terms [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	5	5
Troubled debt restructuring loans	508	802	804
Loans Currently Paying Under Restructured Terms [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	5	4
Troubled debt restructuring loans	1,881	1,735	1,481
Loans Currently Paying Under Restructured Terms [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	14	16	15
Troubled debt restructuring loans	6,550	8,947	9,540
Loans Currently Paying Under Restructured Terms [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	31	28	26
Troubled debt restructuring loans	7,282	7,254	8,068
Loans Currently Paying Under Restructured Terms [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2
Troubled debt restructuring loans	37
Loans that have Defaulted Under Restructured Terms [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	24	6	4
Troubled debt restructuring loans	3,916	5,177	3,390
Loans that have Defaulted Under Restructured Terms [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4
Troubled debt restructuring loans	546
Loans that have Defaulted Under Restructured Terms [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3
Troubled debt restructuring loans	74
Loans that have Defaulted Under Restructured Terms [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	3	1
Troubled debt restructuring loans	2,001	4,149	2,770
Loans that have Defaulted Under Restructured Terms [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	11	2	3
Troubled debt restructuring loans	1,293	1,022	620
Loans that have Defaulted Under Restructured Terms [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	$ 2	$ 6