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, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 11,326	$ 18,171
Specific Allocation	96,800	92,728	$ 83,936
Real Estate Asset [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	4,240	7,833
Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,683	6,625
Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	403	3,713
Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	4,152	6,597
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans		2,213
Specific Allocation	7,483	6,416	7,550
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	632	1,263
Specific Allocation	33,080	30,190	16,807
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	800
Specific Allocation	3,950	3,778	3,454
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	638	420
Specific Allocation	3,414	3,275	1,051
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	189	481
Specific Allocation	4,914	4,092	3,048
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	140	9
Specific Allocation	1,646	1,418	1,567
Real Estate [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	2,449	7,740
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
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	632	1,263
Real Estate [Member] | Real Estate Asset [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	800
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	638	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	189	481
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	140	9
Real Estate [Member] | Real Estate Asset [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,841	3,447
Real Estate [Member] | Business Assets [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	593	701
Real Estate [Member] | Other Assets [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	15	3,592
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation		870
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	250	333
Real Estate [Member] | Specific Allocation [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	225
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	134	45
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	62	207
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	140	9
Real Estate [Member] | Specific Allocation [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	1,386	3,114
Commercial Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,331	5,928
Specific Allocation	22,745	25,106	25,565
Commercial Non-real Estate [Member] | Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,090	5,924
Commercial Non-real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	241	4
Commercial Non-real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	1,867	1,938
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	147	117
Specific Allocation	4,401	4,132	$ 3,694
Consumer Non-real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	147	117
Consumer Non-real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	$ 88	$ 81