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Loans (Impaired Loans) - Additional Information (Detail)	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	May 31, 2020 Loan	Jun. 30, 2020 USD ($) Contract	Mar. 31, 2020 Contract	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Contract Loan	Jun. 30, 2019 USD ($) Loan	Dec. 31, 2019 USD ($) Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional funds available to be advanced in connection with impaired loans		$ 159,000			$ 159,000
Impaired loans classified as troubled debt restructured		$ 6,400,000		$ 981,000	$ 6,400,000	$ 981,000	$ 1,000,000.0
Number of contracts modified | Loan					5		4
TDR impaired loans paid off | Loan	1					0
TDR loans, subsequently defaulted during the period		0		0	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						120 days
Delinquent period for charging down commercial and agricultural credits						120 days
Foreclosed residential real estate property		$ 135,000			$ 135,000		$ 214,000
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans classified as troubled debt restructured		481,000			$ 481,000
Number of contracts modified | Contract					2
TDR impaired loans paid off | Loan					1
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed residential real estate property		0		$ 143,000	$ 0	$ 143,000
Residential real estate properties foreclosure proceedings		$ 854,000		$ 571,000	$ 854,000	$ 571,000
Principal Forgiveness [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of contracts modified | Contract					0
Payment Changes from Monthly Payment to Principal and Interest at Maturity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of contracts modified | Contract			2
Loan maturity date			Jun. 19, 2020
Rate Concession Along With the Amortization Extended [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of contracts modified | Contract		3

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