Investment Securities - Summary of Amortized Cost and Estimated Market Value of Investment Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, due in one year or less	$ 20
Amortized Cost, due after one year through five years	8,936
Amortized Cost, due after five years through ten years	12,366
Amortized Cost, due after ten years	23,543
Amortized Cost	44,865	$ 46,423
Market Value, due in one year or less	20
Market Value, due after one year through five years	8,870
Market Value, due after five years through ten years	12,330
Market Value, due after ten years	23,462
Market Value, total	$ 44,682