Investments - Schedule of Investments in Fixed Maturity Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, Single Maturity Date	$ 8,000	$ 8,100
Cost	30,632	31,042
Gross Unrealized Gains	4	12
Gross Unrealized Losses	(321)	(206)
Fair Value	30,315	30,848
U.S. Treasury securities, obligations of U.S. Government agencies and Municipalities
Schedule of Available-for-sale Securities [Line Items]
Cost	29,560	29,970
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(318)	(206)
Fair Value	29,242	29,764
Corporate debt
Schedule of Available-for-sale Securities [Line Items]
Cost	1,072	1,072
Gross Unrealized Gains	4	12
Gross Unrealized Losses	(3)	0
Fair Value	$ 1,073	$ 1,084