Loans Held for Investment and Allowance for Credit Losses on Loans - Collateral-dependent Gross Loans Held for Investment by Collateral Type and Related Specific Allocation (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 18,171	$ 24,857
Specific Allocation	92,728	83,936	$ 91,366
Real Estate Asset [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	7,833	13,129
Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,625	6,472
Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	3,713	5,256
Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	6,597	7,923
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	2,213	1,952
Specific Allocation	6,412	7,568	8,470
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,263	1,404
Specific Allocation	30,192	16,987	12,318
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	3,778	3,490	2,723
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	420
Specific Allocation	3,276	1,092	726
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	481	871
Specific Allocation	4,098	3,076	2,822
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	9	199
Specific Allocation	1,845	2,104	2,236
Real Estate [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	3,447	8,703
Real Estate [Member] | Real Estate Asset [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	2,213	1,952
Real Estate [Member] | Real Estate Asset [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,263	1,404
Real Estate [Member] | Real Estate Asset [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	420
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	481	871
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	9	199
Real Estate [Member] | Real Estate Asset [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	3,447	8,703
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	870	576
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	333	263
Real Estate [Member] | Specific Allocation [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	45
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	207	143
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	9	178
Real Estate [Member] | Specific Allocation [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	831	1,805
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	10,221	11,674
Specific Allocation	27,311	28,085	34,643
Commercial and Agricultural Non-Real Estate [Member] | Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,625	6,472
Commercial and Agricultural Non-Real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	3,596	5,202
Commercial and Agricultural Non-Real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	4,221	4,938
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	117	54
Specific Allocation	4,135	3,734	$ 3,542
Consumer Non-real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	117	54
Consumer Non-real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	$ 81	$ 20