Loans - Summary of Trouble Debt Restructuring by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 20,200	$ 23,900	$ 23,300
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	64	55	51
Troubled debt restructuring loans	17,024	18,744	19,893
Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	5	5
Troubled debt restructuring loans	521	802	804
Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	8	5	4
Troubled debt restructuring loans	1,926	1,735	1,481
Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	16	16	15
Troubled debt restructuring loans	6,693	8,947	9,540
Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	35	28	27
Troubled debt restructuring loans	7,871	7,254	8,068
Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	13	6
Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	16	5	3
Troubled debt restructuring loans	3,150	5,171	3,390
Non-Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3
Troubled debt restructuring loans	533
Non-Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	29
Non-Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	1
Troubled debt restructuring loans	1,858	4,149	2,770
Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	7	2	2
Troubled debt restructuring loans	704	1,022	620
Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2
Troubled debt restructuring loans	$ 26