Loans (Impaired Loans) - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) Contract	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Loan Contract	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional funds available to be advanced in connection with impaired loans	$ 5,000		$ 5,000
Impaired loans classified as troubled debt restructured	$ 1,100,000	$ 207,000	$ 1,100,000	$ 207,000	$ 178,000
Number of new loans considered TDR | Loan			5		0
TDR loans, subsequently defaulted during the period	0	0	0	0
TDR impaired loans paid off	$ 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	$ 351,000		$ 351,000		$ 600,000
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of new loans considered TDR | Contract	1		1
Foreclosed residential real estate property	$ 187,000	$ 68,000	$ 187,000	$ 68,000
Residential real estate properties foreclosure proceedings	$ 379,000	$ 174,000	$ 379,000	$ 174,000