Loans - Summary of Troubled Debt Restructuring by Loan Class, Classified Separately Under Terms (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 Contract	Dec. 31, 2012 Contract	Mar. 31, 2012 Contract
Loans Currently Paying Under Restructured Terms [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	52	54	48
Troubled debt restructuring loans	$ 18,513	$ 18,738	$ 28,060
Loans Currently Paying Under Restructured Terms [Member] | Commercial, financial & agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	5
Troubled debt restructuring loans	799	802
Loans Currently Paying Under Restructured Terms [Member] | Real estate - construction & development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	5	7
Troubled debt restructuring loans	1,883	1,735	2,413
Loans Currently Paying Under Restructured Terms [Member] | Real estate - commercial & farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	16	16	19
Troubled debt restructuring loans	8,878	8,947	17,869
Loans Currently Paying Under Restructured Terms [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
Loans Currently Paying Under Restructured Terms [Member] | Consumer installment loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans
Loans that have Defaulted Under Restructured Terms [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	8	6	7
Troubled debt restructuring loans	4,755	5,177	3,655
Loans that have Defaulted Under Restructured Terms [Member] | Commercial, financial & agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans
Loans that have Defaulted Under Restructured Terms [Member] | Real estate - construction & development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		3
Troubled debt restructuring loans	43		518
Loans that have Defaulted Under Restructured Terms [Member] | Real estate - commercial & farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	1
Troubled debt restructuring loans	3,595	4,149	2,072
Loans that have Defaulted Under Restructured Terms [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
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	$ 6	$ 6