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, 2021	Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 24,857	$ 20,803
Real Estate Asset [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	13,129	11,808
Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,472	8,473
Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	5,256	522
Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	7,923	6,212
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,952	848
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,404	4,719
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	871	2,117
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	199	866
Real Estate [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	8,703	3,258
Real Estate [Member] | Real Estate Asset [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,952	848
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	1,404	4,719
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	871	2,117
Real Estate [Member] | Real Estate Asset [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	199	866
Real Estate [Member] | Real Estate Asset [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	8,703	3,258
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	576	226
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	263	1,000
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	143	373
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	178	616
Real Estate [Member] | Specific Allocation [Member] | Farmland [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,805	1,114
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	11,565	8,873
Commercial and Agricultural Non-Real Estate [Member] | Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,363	8,460
Commercial and Agricultural Non-Real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	5,202	413
Commercial and Agricultural Non-Real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	4,867	2,813
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	54	109
Consumer Non-real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	54	109
Consumer Non-real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	20	58
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	109	13
Other Loans [Member] | Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	109	13
Other Loans [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 71	$ 12