Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($) Contract	Jun. 30, 2022 USD ($) Contract	Jun. 30, 2021 USD ($) Contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		7	2	14
Total Pre-Modification Outstanding Recorded Investment	$ 0	$ 6,797	$ 69	$ 13,353
Post- Modification Outstanding Recorded Investment		4,114	68	10,539
Troubled Debt Restructuring [Policy Text Block]		$ 0	$ 0	$ 1,091
Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		1		3
Total Pre-Modification Outstanding Recorded Investment		$ 6,596		$ 12,969
Post- Modification Outstanding Recorded Investment		3,916		10,167
Troubled Debt Restructuring [Policy Text Block]		$ 0		$ 1,091
Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		4	2	7
Total Pre-Modification Outstanding Recorded Investment		$ 172	$ 69	$ 291
Post- Modification Outstanding Recorded Investment		169	68	287
Troubled Debt Restructuring [Policy Text Block]		$ 0	$ 0	$ 0
Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		2		4
Total Pre-Modification Outstanding Recorded Investment		$ 29		$ 93
Post- Modification Outstanding Recorded Investment		29		85
Troubled Debt Restructuring [Policy Text Block]		$ 0		$ 0
Time and Demand Loans | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		1		3
Total Pre-Modification Outstanding Recorded Investment		$ 6,596		$ 12,969
Post- Modification Outstanding Recorded Investment		3,916		10,167
Troubled Debt Restructuring [Policy Text Block]		$ 0		$ 1,091
Senior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract		4	2	6
Total Pre-Modification Outstanding Recorded Investment		$ 172	$ 69	$ 277
Post- Modification Outstanding Recorded Investment		169	68	274
Troubled Debt Restructuring [Policy Text Block]		$ 0	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		4
Total Pre-Modification Outstanding Recorded Investment		$ 29		$ 93
Post- Modification Outstanding Recorded Investment		29		85
Troubled Debt Restructuring [Policy Text Block]		0		0
Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0	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		0		6,373
Extended Maturity [Member] | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0	0	0
Extended Maturity [Member] | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0		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		0		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	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		0
Contractual Interest Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		29	10	198
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		0
Contractual Interest Rate Reduction [Member] | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0	10	105
Contractual Interest Rate Reduction [Member] | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		29		93
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		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		0	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		29		93
Contractual Payment Modification [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		6,768	59	6,782
Contractual Payment Modification [Member] | Commercial, financial, agricultural and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		6,596		6,596
Contractual Payment Modification [Member] | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		172	59	186
Contractual Payment Modification [Member] | Loans to individuals [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		0		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		6,596		6,596
Contractual Payment Modification [Member] | Senior Lien | Residential real estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Pre-Modification Outstanding Recorded Investment		172	$ 59	172
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		$ 0