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Loans (Impaired Loans) - Additional Information (Detail)		3 Months Ended		9 Months Ended
	Jul. 30, 2021	Sep. 30, 2023 USD ($) Contract	Sep. 30, 2022 USD ($) Contract	Sep. 30, 2023 USD ($) Contract	Jun. 30, 2023 USD ($)	Jan. 01, 2023 USD ($)	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans classified as troubled debt restructured			$ 4,000,000				$ 3,600,000
Number of contracts modified | Contract		0	3
Term of loan	5 years
Allowance for loan losses		$ 25,277,000		$ 25,277,000	$ 24,910,000		20,313,000
Modifications to borrower experiencing financial difficulty | Contract		0	0
Maximum time for re-evaluation (in months)				12 months
Re-evaluation period for real estate				2 years
Unsecured consumer loans, credit card credits and overdraft lines of credit reach				90 days
Delinquent period for charging down consumer loans				90 days
Litigation and any deficiency charged off period				150 days
Delinquent period for charging down/allocated commercial and agricultural credits				120 days
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 315,000		$ 315,000	237,000		349,000
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		16,805,000		16,805,000	16,681,000		11,924,000
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		3,842,000		3,842,000	$ 3,998,000		998,000
Foreclosed residential real estate property		0	$ 0	0			$ 0
Residential real estate properties foreclosure proceedings		$ 92,000	$ 211,000	$ 92,000
ASU 2016-13 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses and unfunded commitment liability						$ 4,500,000
Allowance for redit losses and unfunded commitment liability, net of tax						$ 3,400,000
Principal Forgiveness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of contracts modified | Contract		0		0

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