Other Real Estate Owned and Other Repossessed Assets - Expenses Related to Foreclosed and Repossessed Assets (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Real Estate And Foreclosed Assets [Abstract]
Net loss on sales	$ 152,000	$ 109,000	$ 158,000
Provision for (recovery of) unrealized losses	37,000	(16,000)	287,000
Operating expenses, net of rental income	135,000	191,000	338,000
Total Expenses	$ 324,000	$ 284,000	$ 783,000