Allowances for Loan Losses - Summary of Allowances for Loan Losses by Loan Class (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	$ 3,152	$ 2,789
Charge-offs	0	52
Recoveries	11	3
Provision	280	47
Ending balance	3,443	2,787
Agriculture Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	23	120
Charge-offs	0	0
Recoveries	0	0
Provision	(3)	(15)
Ending balance	20	105
Commercial Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	582	290
Charge-offs	0	0
Recoveries	2	0
Provision	1	(25)
Ending balance	585	315
Commercial Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	799	314
Charge-offs	0	0
Recoveries	0	0
Provision	271	1
Ending balance	1,070	315
Residential Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	1,634	1,702
Charge-offs	0	49
Recoveries	7	2
Provision	87	19
Ending balance	1,728	1,674
Consumer Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	22	35
Charge-offs	0	3
Recoveries	2	1
Provision	(11)	(9)
Ending balance	13	24
Municipal Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	15	18
Charge-offs	0	0
Recoveries	0	0
Provision	0	0
Ending balance	15	18
Unallocated [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	77	310
Charge-offs	0	0
Recoveries	0	0
Provision	(65)	(26)
Ending balance	$ 12	$ 336