Allowances for Loan Losses - Summary of Classes of the Loan Portfolio Summarized by the Internal Risk Rating System (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	$ 668,672	$ 236,840
Agriculture Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	8,873	11,246
Commercial Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	123,536	21,534
Commercial Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	309,079	27,261
Residential Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	216,526	167,536
Consumer Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	4,309	2,514
Municipal Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	6,351	6,749
Pass [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	656,289	235,997
Pass [Member] | Agriculture Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	8,873	11,246
Pass [Member] | Commercial Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	118,991	21,259
Pass [Member] | Commercial Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	302,878	27,261
Pass [Member] | Residential Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	214,889	166,968
Pass [Member] | Consumer Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	4,309	2,514
Pass [Member] | Municipal Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	6,351	6,749
Special Mention [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	5,170	0
Special Mention [Member] | Agriculture Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Special Mention [Member] | Commercial Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	2,935	0
Special Mention [Member] | Commercial Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	1,925	0
Special Mention [Member] | Residential Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	310	0
Special Mention [Member] | Consumer Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Special Mention [Member] | Municipal Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Substandard [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	7,213	843
Substandard [Member] | Agriculture Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Substandard [Member] | Commercial Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	1,610	275
Substandard [Member] | Commercial Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	4,276	0
Substandard [Member] | Residential Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	1,327	568
Substandard [Member] | Consumer Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Substandard [Member] | Municipal Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member] | Agriculture Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member] | Commercial Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member] | Commercial Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member] | Residential Real Estate Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member] | Consumer Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	0	0
Doubtful [Member] | Municipal Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	$ 0	$ 0