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, 2014 Contract	Sep. 30, 2013 Contract	Sep. 30, 2014 Contract	Sep. 30, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	27	25	60	57
Extend Maturity	$ 0	$ 3,277	$ 1,505	$ 4,083
Modify Rate	172	60	549	664
Modify Payments	1,131	1,934	1,817	3,236
Total Pre-Modification Outstanding Recorded Investment	1,303	5,271	3,871	7,983
Post- Modification Outstanding Recorded Investment	1,253	3,272	3,846	5,532
Financing Receivable Specific Reserve				1,534
Specific Reserve	2000	1260000	49000
Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		4	2	7
Extend Maturity		2,442	1,505	2,969
Modify Rate		0	0	0
Modify Payments		93	0	105
Total Pre-Modification Outstanding Recorded Investment		2,535	1,505	3,074
Post- Modification Outstanding Recorded Investment		601	1,648	1,041
Financing Receivable Specific Reserve				198
Specific Reserve		198	27
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	24	10	44	32
Extend Maturity	0	67	0	347
Modify Rate	164	24	468	350
Modify Payments	1,116	269	1,767	1,552
Total Pre-Modification Outstanding Recorded Investment	1,280	360	2,235	2,249
Post- Modification Outstanding Recorded Investment	1,233	361	2,091	1,924
Financing Receivable Specific Reserve				274
Specific Reserve	2	0	22
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		5	1	6
Extend Maturity		758	0	758
Modify Rate		0	0	244
Modify Payments		1,551	8	1,551
Total Pre-Modification Outstanding Recorded Investment		2,309	8	2,553
Post- Modification Outstanding Recorded Investment		2,252	6	2,484
Specific Reserve		1062	0	1062
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	3	6	13	12
Extend Maturity	0	10	0	9
Modify Rate	8	36	81	70
Modify Payments	15	21	42	28
Total Pre-Modification Outstanding Recorded Investment	23	67	123	107
Post- Modification Outstanding Recorded Investment	20	58	101	83
Financing Receivable Specific Reserve				$ 0
Specific Reserve	0	0	0