Other Real Estate Owned and Other Repossessed Assets - Real Estate Owned and Other Repossessed Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Other Real Estate And Foreclosed Assets [Abstract]
Real estate owned and other repossessed assets	$ 1,125		$ 1,656
Valuation allowance	(248)	$ (287)	(403)	$ (389)	$ (549)	$ (1,012)
End of period	$ 877		$ 1,253