Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) Contract	Mar. 31, 2021 USD ($) Contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	2	7
Total Pre-Modification Outstanding Recorded Investment	$ 69	$ 6,556
Post- Modification Outstanding Recorded Investment	69	6,519
Troubled Debt Restructuring [Policy Text Block]	$ 0	$ 1,190
Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		2
Total Pre-Modification Outstanding Recorded Investment		$ 6,373
Post- Modification Outstanding Recorded Investment		6,339
Troubled Debt Restructuring [Policy Text Block]		$ 1,190
Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	2	3
Total Pre-Modification Outstanding Recorded Investment	$ 69	$ 119
Post- Modification Outstanding Recorded Investment	69	119
Troubled Debt Restructuring [Policy Text Block]	$ 0	$ 0
Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		2
Total Pre-Modification Outstanding Recorded Investment		$ 64
Post- Modification Outstanding Recorded Investment		61
Troubled Debt Restructuring [Policy Text Block]		$ 0
Time and Demand Loans | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		2
Total Pre-Modification Outstanding Recorded Investment		$ 6,373
Post- Modification Outstanding Recorded Investment		6,339
Troubled Debt Restructuring [Policy Text Block]		$ 1,190
Senior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	2	2
Total Pre-Modification Outstanding Recorded Investment	$ 69	$ 105
Post- Modification Outstanding Recorded Investment	69	106
Troubled Debt Restructuring [Policy Text Block]	0	$ 0
Junior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		1
Total Pre-Modification Outstanding Recorded Investment		$ 14
Post- Modification Outstanding Recorded Investment		13
Troubled Debt Restructuring [Policy Text Block]		$ 0
Automobiles | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		2
Total Pre-Modification Outstanding Recorded Investment		$ 64
Post- Modification Outstanding Recorded Investment		61
Troubled Debt Restructuring [Policy Text Block]		0
Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	6,373
Extended Maturity [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		6,373
Extended Maturity [Member] | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0
Extended Maturity [Member] | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Extended Maturity [Member] | Time and Demand Loans | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		6,373
Extended Maturity [Member] | Senior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	0	0
Extended Maturity [Member] | Junior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Extended Maturity [Member] | Automobiles | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Interest Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	10	169
Contractual Interest Rate Reduction [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Interest Rate Reduction [Member] | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	10	105
Contractual Interest Rate Reduction [Member] | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		64
Contractual Interest Rate Reduction [Member] | Time and Demand Loans | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Interest Rate Reduction [Member] | Senior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	10	105
Contractual Interest Rate Reduction [Member] | Junior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Interest Rate Reduction [Member] | Automobiles | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		64
Contractual Payment Modification [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	59	14
Contractual Payment Modification [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Payment Modification [Member] | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	59	14
Contractual Payment Modification [Member] | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Payment Modification [Member] | Time and Demand Loans | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0
Contractual Payment Modification [Member] | Senior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment	$ 59	0
Contractual Payment Modification [Member] | Junior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		14
Contractual Payment Modification [Member] | Automobiles | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		$ 0