Fair Value of Instruments - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest-bearing deposits maturing date	90 days
Collateral dependent impaired loans categorized as Level 3	$ 1,979	$ 1,852	$ 1,406
Specific allocation for impaired loans	123	135	$ 125
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans categorized as Level 3	$ 562	$ 576