Other Real Estate Owned and Other Repossessed Assets - Valuation Allowance Related to Real Estate Owned (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Real Estate And Foreclosed Assets [Abstract]
Beginning of period	$ 287,000	$ 549,000	$ 403,000	$ 1,012,000
Additions (recoveries) charged to expense	10,000	0	33,000	(38,000)
Sales of real estate owned with a valuation allowance	(49,000)	(160,000)	(188,000)	(585,000)
End of period	$ 248,000	$ 389,000	$ 248,000	$ 389,000