Other Real Estate Owned and Other Repossessed Assets - Valuation Allowance Related to Real Estate Owned (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Real Estate And Foreclosed Assets [Abstract]
Beginning of period	$ 158,000	$ 248,000	$ 308,000	$ 403,000
Additions charged to expense	26,000	49,000	62,000	82,000
Sales of real estate owned with a valuation allowance	(14,000)		(200,000)	(188,000)
End of period	$ 170,000	$ 297,000	$ 170,000	$ 297,000