Commitments, Contingencies and Off-Balance-Sheet Risk - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Maximum period of commitments to make loans	1 year
Maximum time period of maturities	30 years
Average reserve balance under Federal Reserve Board requirements	$ 4,112	$ 2,887
Minimum [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Range of fixed interest rate loan commitments	2.88%	3.25%
Maximum [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Range of fixed interest rate loan commitments	10.25%	8.50%