Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Contract	Sep. 30, 2012 Contract	Sep. 30, 2013 Contract	Sep. 30, 2012 Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	25	7	57	15
Extend Maturity	$ 3,277	$ 1,153	$ 4,083	$ 2,422
Modify Rate	60	685	664	800
Modify Payments	1,934	1,509	3,236	7,621
Total Pre-Modification Outstanding Recorded Investment	5,271	3,347	7,983	10,843
Post- Modification Outstanding Recorded Investment	3,272	3,533	5,532	10,336
Financing Receivable Specific Reserve				3,238
Specific Reserve	1260000	844000	1534000
Recorded Investment	14	0	18	0
Number of Contracts	2	0	3	0
Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	4	6	7	10
Extend Maturity	2,442	1,153	2,969	1,599
Modify Rate	0	169	0	187
Modify Payments	93	1,509	105	7,538
Total Pre-Modification Outstanding Recorded Investment	2,535	2,831	3,074	9,324
Post- Modification Outstanding Recorded Investment	601	3,004	1,041	8,885
Financing Receivable Specific Reserve				3,140
Specific Reserve	198	746	198
Real estate construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts				1
Extend Maturity				823
Modify Rate				0
Modify Payments				0
Total Pre-Modification Outstanding Recorded Investment				823
Post- Modification Outstanding Recorded Investment				791
Financing Receivable Specific Reserve				0
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	10		32	3
Extend Maturity	67		347	0
Modify Rate	24		350	97
Modify Payments	269		1,552	83
Total Pre-Modification Outstanding Recorded Investment	360		2,249	180
Post- Modification Outstanding Recorded Investment	361		1,924	131
Financing Receivable Specific Reserve				0
Specific Reserve	0		274
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	5	1	6	1
Extend Maturity	758	0	758	0
Modify Rate	0	516	244	516
Modify Payments	1,551	0	1,551	0
Total Pre-Modification Outstanding Recorded Investment	2,309	516	2,553	516
Post- Modification Outstanding Recorded Investment	2,252	529	2,484	529
Specific Reserve	1062	98	1062	98
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	6		12
Extend Maturity	10		9
Modify Rate	36		70
Modify Payments	21		28
Total Pre-Modification Outstanding Recorded Investment	67		107
Post- Modification Outstanding Recorded Investment	58		83
Specific Reserve	0		0
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modification, Subsequent Default, Number of Contracts	1		1
Recorded Investment	9	0	9	0
Number of Contracts		0		0
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modification, Subsequent Default, Number of Contracts	1		2
Recorded Investment	$ 5	$ 0	$ 9	$ 0
Number of Contracts		0		0