Allowance for Loan Losses - Impaired Loans Excluding Purchased-Credit Impaired ("PCI") Loans - Recorded Investment and Unpaid Principal Balances (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 1,234	$ 2,338
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,259	2,363
Impaired financing receivables, with an allowance recorded, Recorded Investment	244	328
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	248	332
Impaired financing receivables, with an allowance recorded, Related Allowance	26	107
Impaired financing receivables, Recorded Investment, Total	1,478	2,666
Impaired financing receivables, Unpaid Principal Balance, Total	1,507	2,695
Impaired financing receivables, Related Allowance, Total	26	107
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with an allowance recorded, Recorded Investment		74
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance		74
Impaired financing receivables, with an allowance recorded, Related Allowance		73
Impaired financing receivables, Recorded Investment, Total		74
Impaired financing receivables, Unpaid Principal Balance, Total		74
Impaired financing receivables, Related Allowance, Total		73
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	86	757
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	86	757
Impaired financing receivables, with an allowance recorded, Recorded Investment	213	223
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	213	223
Impaired financing receivables, with an allowance recorded, Related Allowance	8	5
Impaired financing receivables, Recorded Investment, Total	299	980
Impaired financing receivables, Unpaid Principal Balance, Total	299	980
Impaired financing receivables, Related Allowance, Total	8	5
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	30	48
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	30	48
Impaired financing receivables, Recorded Investment, Total	30	48
Impaired financing receivables, Unpaid Principal Balance, Total	30	48
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	526	915
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	551	940
Impaired financing receivables, with an allowance recorded, Recorded Investment	31	31
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	35	35
Impaired financing receivables, with an allowance recorded, Related Allowance	18	29
Impaired financing receivables, Recorded Investment, Total	557	946
Impaired financing receivables, Unpaid Principal Balance, Total	586	975
Impaired financing receivables, Related Allowance, Total	18	29
Farm Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	592	618
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	592	618
Impaired financing receivables, Recorded Investment, Total	592	618
Impaired financing receivables, Unpaid Principal Balance, Total	$ 592	$ 618