Investments - Schedule of Investments in Fixed Maturity Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, Single Maturity Date	$ 8,100	$ 8,100
Cost	22,344	31,042
Gross Unrealized Gains	3	12
Gross Unrealized Losses	(464)	(206)
Fair Value	21,883	30,848
U.S. Treasury securities, obligations of U.S. Government agencies and Municipalities
Schedule of Available-for-sale Securities [Line Items]
Cost	21,722	29,970
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(462)	(206)
Fair Value	21,263	29,764
Corporate debt
Schedule of Available-for-sale Securities [Line Items]
Cost	622	1,072
Gross Unrealized Gains	0	12
Gross Unrealized Losses	(2)	0
Fair Value	$ 620	$ 1,084