Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) Contract	Sep. 30, 2015 USD ($) Contract	Sep. 30, 2016 USD ($) Contract	Sep. 30, 2015 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	17	11	57	37
Total Pre-Modification Outstanding Recorded Investment	$ 4,463	$ 1,016	$ 12,186	$ 4,217
Post- Modification Outstanding Recorded Investment	$ 4,424	$ 996	$ 11,262	$ 3,963
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	1612000	0	1680000	52000
Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	1	1	5	4
Total Pre-Modification Outstanding Recorded Investment	$ 3,853	$ 543	$ 7,955	$ 2,403
Post- Modification Outstanding Recorded Investment	$ 3,853	$ 525	$ 7,281	$ 2,314
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	1612	0	1612	52
Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	11	8	35	24
Total Pre-Modification Outstanding Recorded Investment	$ 473	$ 455	$ 2,762	$ 1,254
Post- Modification Outstanding Recorded Investment	$ 441	$ 455	$ 2,620	$ 1,165
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0	0	0	0
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	1		7	1
Total Pre-Modification Outstanding Recorded Investment	$ 85		$ 1,373	$ 464
Post- Modification Outstanding Recorded Investment	$ 85		$ 1,285	$ 407
Financing Receivable, Modifications, Determination of Allowance for Credit Losses	0		68	0
Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	4	2	10	8
Total Pre-Modification Outstanding Recorded Investment	$ 52	$ 18	$ 96	$ 96
Post- Modification Outstanding Recorded Investment	$ 45	$ 16	$ 76	$ 77
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	$ 85	$ 0	$ 1,441	$ 1,751
Extended Maturity [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0	93	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	85		1,348	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	142	0	4,294	357
Contractual Interest Rate Reduction [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0	4,009	0
Contractual Interest Rate Reduction [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	100	0	214	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	42	0	71	61
Contractual Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	4,236	1,016	6,451	2,109
Contractual Payment Modification [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	3,853	543	3,853	652
Contractual Payment Modification [Member] | Residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	373	455	2,548	958
Contractual Payment Modification [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0		25	464
Contractual Payment Modification [Member] | Loans to individuals [Member]
Financing Receivable, Modifications [Line Items]
Total Pre-Modification Outstanding Recorded Investment	$ 10	$ 18	$ 25	$ 35