Stockholders' Equity - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ (3,092)	$ (2,702)
Accumulated Net Unrealized Investment Gain (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized or unamortized gains (losses)	(4,141)	(4,376)
Tax effect	1,049	1,674
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(1,342)	(926)
Available for Sale Securities [Member] | Accumulated Net Unrealized Investment Gain (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized or unamortized gains (losses)	(1,797)	(1,500)
Tax effect	455	574
Held to Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(1,750)	(1,776)
Held to Maturity Securities [Member] | Accumulated Net Unrealized Investment Gain (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized or unamortized gains (losses)	(2,344)	(2,876)
Tax effect	$ 594	$ 1,100