Loans and Allowance for Loan Losses - Summary of Trouble Debt Restructuring by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Finance Receivable Transferred To Held For Sale [Line Items]
Troubled debt restructuring loans	$ 23,900	$ 26,100
Accruing Loans [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	55	39
Troubled debt restructuring loans	18,744	17,951
Accruing Loans [Member] | Commercial, financial & agricultural [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	5
Troubled debt restructuring loans	802
Accruing Loans [Member] | Real estate - construction & development [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	5	6
Troubled debt restructuring loans	1,735	1,774
Accruing Loans [Member] | Real estate - commercial and farmland [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	16	14
Troubled debt restructuring loans	8,947	9,622
Accruing Loans [Member] | Real estate - residential [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	28	19
Troubled debt restructuring loans	7,254	6,555
Accruing Loans [Member] | Consumer installment loans [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	1
Troubled debt restructuring loans	6
Non-Accruing Loans [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	5	11
Troubled debt restructuring loans	5,171	8,155
Non-Accruing Loans [Member] | Real estate - construction & development [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts		5
Troubled debt restructuring loans		2,122
Non-Accruing Loans [Member] | Real estate - commercial and farmland [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	3	2
Troubled debt restructuring loans	4,149	4,737
Non-Accruing Loans [Member] | Real estate - residential [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Number of contracts	2	4
Troubled debt restructuring loans	$ 1,022	$ 1,296