Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) Contract	Jun. 30, 2014 USD ($) Contract	Jun. 30, 2015 USD ($) Contract	Jun. 30, 2014 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Financing Receivable Modification Number Of Contracts | Contract	18	13
Number of Contracts | Contract			26	34
Total Pre-Modification Outstanding Recorded Investment			$ 3,201	$ 2,527
Post- Modification Outstanding Recorded Investment			$ 3,029	$ 2,450
Financing Receivable Modifications Extend Maturity	$ 252	$ 1,420
Financing Receivable Modifications Modify Rate	106	162
Financing Receivable Modifications Modify Payments	594	133
Financing Receivable, Modifications, Pre-Mod Recorded Investment	952	1,715
Financing Receivable, Modification, Post-Modification Recorded Investment	$ 898	$ 1,718
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	60000	2000	60000	68000
Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable Modification Number Of Contracts | Contract	2	1
Number of Contracts | Contract			3	2
Total Pre-Modification Outstanding Recorded Investment			$ 1,860	$ 1,480
Post- Modification Outstanding Recorded Investment			$ 1,812	$ 1,463
Financing Receivable Modifications Extend Maturity	$ 252	$ 1,420
Financing Receivable Modifications Modify Rate	0	0
Financing Receivable Modifications Modify Payments	109	0
Financing Receivable, Modifications, Pre-Mod Recorded Investment	361	1,420
Financing Receivable, Modification, Post-Modification Recorded Investment	$ 317	$ 1,433
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	53	0	53	20
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable Modification Number Of Contracts | Contract	11	8
Number of Contracts | Contract			16	21
Total Pre-Modification Outstanding Recorded Investment			$ 799	$ 935
Post- Modification Outstanding Recorded Investment			$ 723	$ 895
Financing Receivable Modifications Extend Maturity	$ 0	$ 0
Financing Receivable Modifications Modify Rate	45	120
Financing Receivable Modifications Modify Payments	485	126
Financing Receivable, Modifications, Pre-Mod Recorded Investment	530	246
Financing Receivable, Modification, Post-Modification Recorded Investment	$ 525	$ 243
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	7	2	7	48
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract			1	1
Total Pre-Modification Outstanding Recorded Investment			$ 463	$ 12
Post- Modification Outstanding Recorded Investment			$ 428	$ 7
Financing Receivable, Modifications, Determination of Allowance for Credit Losses			0	0
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable Modification Number Of Contracts | Contract	5	4
Number of Contracts | Contract			6	10
Total Pre-Modification Outstanding Recorded Investment			$ 79	$ 100
Post- Modification Outstanding Recorded Investment			$ 66	$ 85
Financing Receivable Modifications Extend Maturity	$ 0	$ 0
Financing Receivable Modifications Modify Rate	61	42
Financing Receivable Modifications Modify Payments	0	7
Financing Receivable, Modifications, Pre-Mod Recorded Investment	61	49
Financing Receivable, Modification, Post-Modification Recorded Investment	$ 56	$ 42
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0	0	0
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			$ 1,751	$ 1,480
Extended Maturity [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			1,751	1,480
Extended Maturity [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			0	0
Extended Maturity [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			0	0
Extended Maturity [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			0	0
Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			357	364
Contractual Interest Rate Reduction [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			0	0
Contractual Interest Rate Reduction [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			296	291
Contractual Interest Rate Reduction [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			0	0
Contractual Interest Rate Reduction [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			61	73
Contractual Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			1,093	683
Contractual Payment Modification [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			109	0
Contractual Payment Modification [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			503	644
Contractual Payment Modification [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			463	12
Contractual Payment Modification [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment			$ 18	$ 27