Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) Contract	Jun. 30, 2015 USD ($) Contract	Jun. 30, 2016 USD ($) Contract	Jun. 30, 2015 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	27	18	42	26
Total Pre-Modification Outstanding Recorded Investment	$ 2,982	$ 952	$ 7,960	$ 3,201
Post- Modification Outstanding Recorded Investment	$ 2,833	$ 898	$ 7,405	$ 3,029
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	114000	60000	114000	60000
Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	4	2	5	3
Total Pre-Modification Outstanding Recorded Investment	$ 332	$ 361	$ 4,101	$ 1,860
Post- Modification Outstanding Recorded Investment	$ 217	$ 317	$ 3,708	$ 1,812
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	40	53	40	53
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	17	11	26	16
Total Pre-Modification Outstanding Recorded Investment	$ 1,435	$ 530	$ 2,530	$ 799
Post- Modification Outstanding Recorded Investment	$ 1,428	$ 525	$ 2,440	$ 723
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	7	0	7
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	4		6	1
Total Pre-Modification Outstanding Recorded Investment	$ 1,198		$ 1,289	$ 463
Post- Modification Outstanding Recorded Investment	$ 1,173		$ 1,227	$ 428
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	74		74	0
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	2	5	5	6
Total Pre-Modification Outstanding Recorded Investment	$ 17	$ 61	$ 40	$ 79
Post- Modification Outstanding Recorded Investment	$ 15	$ 56	$ 30	$ 66
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	$ 1,290	$ 252	$ 1,356	$ 1,751
Extended Maturity [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	92	252	92	1,751
Extended Maturity [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0	0	0
Extended Maturity [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	1,198		1,264	0
Extended Maturity [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0	0	0
Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	251	106	4,152	357
Contractual Interest Rate Reduction [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	240	0	4,009	0
Contractual Interest Rate Reduction [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	45	114	296
Contractual Interest Rate Reduction [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0		0	0
Contractual Interest Rate Reduction [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	11	61	29	61
Contractual Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	1,441	594	2,452	1,093
Contractual Payment Modification [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	109	0	109
Contractual Payment Modification [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	1,435	485	2,416	503
Contractual Payment Modification [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0		25	463
Contractual Payment Modification [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	$ 6	$ 0	$ 11	$ 18