Regulatory Matters - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jul. 31, 2013
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount available for dividend distribution without prior approval from Regulatory Agency		$ 16.1
Percentage of Bank's capital and surplus of which extensions of credit to a single affiliate are limited		10.00%
Percentage of Bank's capital and surplus of which extensions of credit to all affiliates are limited		20.00%
Basel III New Requirements [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 capital minimum buffer percent			2.50%
Capital conservation buffer requirement phase in period in years		4 years
Minimum Capital Requirements Effective Date		Jan. 01, 2015
Capital Conservation Buffer Above Minimum Risk-based Capital Requirements		0.625%
Basel III New Requirements [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital Conservation Buffer Above Minimum Risk-based Capital Requirements	1.25%