Loans Held for Investment and Allowance for Credit Losses on Loans - Summary of Amounts Included in Nonaccrual Loans Segregated by Portfolio Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	$ 17,453	$ 20,892
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	3,112	2,900
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	407	407
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	104	80
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	2,391	2,763
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	133	280
Real Estate [Member] | Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	4,059	4,224
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	5,956	7,569
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	111	148
Oil and Gas [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total		1,070
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans, Total	$ 1,180	$ 1,451