Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Security Obligation	Dec. 31, 2017 USD ($) Security Obligation
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Number of obligations of state and political subdivisions in an unrealized loss position | Obligation	56	39
Number of obligations of state and political subdivisions | Obligation	82	80
Percentage of investment portfolio	100.00%	100.00%
Weighted-average period of re-pricing of portfolio	4 years 7 months 12 days	4 years 8 months 12 days
Proceeds from maturities, calls, principal payments and sales of securities available for sale	$ 15,694,000	$ 28,157,000
Gross realized gains on securities available for sale		49,000
Gross realized losses on securities available for sale	$ 1,000	$ 152,000
Available-for-sale securities, number of securities donated to not-for-profit organization | Security	0	1
Gross gain on charitable donations of available for sale securities		$ 13,000
Proceeds from maturities, calls and principal payments of securities held to maturity	$ 4,617,000	4,981,000
Gross gains or losses on held to maturity securities	0	0
Securities book value	43,100,000	$ 35,200,000
Impairment recognized	$ 0
U.S. agency and mortgage-backed securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Number of securities in unrealized loss position | Security	83	68
Number of securities | Security	90	82