Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) Contract	Mar. 31, 2015 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	16	8
Total Pre-Modification Outstanding Recorded Investment	$ 4,978	$ 2,249
Post- Modification Outstanding Recorded Investment	$ 4,844	$ 2,139
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0
Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	2	1
Total Pre-Modification Outstanding Recorded Investment	$ 3,769	$ 1,498
Post- Modification Outstanding Recorded Investment	$ 3,749	$ 1,476
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	8	5
Total Pre-Modification Outstanding Recorded Investment	$ 988	$ 269
Post- Modification Outstanding Recorded Investment	$ 910	$ 203
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	3	1
Total Pre-Modification Outstanding Recorded Investment	$ 198	$ 464
Post- Modification Outstanding Recorded Investment	$ 169	$ 449
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	3	1
Total Pre-Modification Outstanding Recorded Investment	$ 23	$ 18
Post- Modification Outstanding Recorded Investment	$ 16	$ 11
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	$ 65	$ 1,498
Extended Maturity [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	1,498
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	65	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	3,901	252
Contractual Interest Rate Reduction [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	3,769	0
Contractual Interest Rate Reduction [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	114	252
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	18	0
Contractual Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	1,012	499
Contractual Payment Modification [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0
Contractual Payment Modification [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	874	17
Contractual Payment Modification [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	133	464
Contractual Payment Modification [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	$ 5	$ 18