Loans - Summary of Trouble Debt Restructuring by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 23,300	$ 23,900	$ 31,700
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	52	55	46
Troubled debt restructuring loans	18,513	18,744	26,848
Accruing Loans [Member] | Commercial, financial & agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	5
Troubled debt restructuring loans	799	802
Accruing Loans [Member] | Real estate - construction & development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	5	6
Troubled debt restructuring loans	1,883	1,735	1,305
Accruing Loans [Member] | Real estate - commercial & farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	16	16	18
Troubled debt restructuring loans	8,878	8,947	17,765
Accruing Loans [Member] | Real estate - residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	26	28	22
Troubled debt restructuring loans	6,953	7,254	7,778
Accruing Loans [Member] | Consumer installment loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1
Troubled debt restructuring loans		6
Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	8	5	9
Troubled debt restructuring loans	4,755	5,171	4,867
Non-Accruing Loans [Member] | Commercial, financial & agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans
Non-Accruing Loans [Member] | Real estate - construction & development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		4
Troubled debt restructuring loans	43		1,626
Non-Accruing Loans [Member] | Real estate - commercial & farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	2
Troubled debt restructuring loans	3,595	4,149	2,176
Non-Accruing Loans [Member] | Real estate - residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	2	3
Troubled debt restructuring loans	1,111	1,022	1,065
Non-Accruing Loans [Member] | Consumer installment loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	$ 6