Other Real Estate Owned and Other Repossessed Assets - Expenses Related to Foreclosed and Repossessed Assets (Detail) - USD ($)	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Real Estate And Foreclosed Assets [Abstract]
Net loss on sales	$ (4,000)	$ 20,000	$ 154,000	$ 128,000
Provision for (recovery of) unrealized losses	49,000	53,000	82,000	15,000	$ 82,000	$ 15,000
Operating expenses, net of rental income	25,000	33,000	95,000	118,000	$ 95,000	$ 118,000
Total expenses	$ 70,000	$ 106,000	$ 331,000	$ 261,000