Loans (Impaired Loans) - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional funds available to be advanced in connection with impaired loans	$ 1,000
Impaired loans classified as troubled debt restructured	$ 102,000	$ 527,000	$ 178,000
TDR loans, subsequently defaulted during the period	0	0
TDR impaired loans paid off	$ 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	$ 510,000		$ 600,000
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed residential real estate property	0	$ 3,000
Residential real estate properties foreclosure proceedings	$ 639,000	$ 49,000