Investments - Amortized Cost and Fair Value of Fixed Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 4,771	$ 16,934
Due after one year through five years	17,341	13,876
Due after five years	232	232
Amortized Cost, Total	22,344	31,042
Fair Value
Due in one year or less	4,732	16,899
Due after one year through five years	16,920	13,708
Due after five years	231	241
Fair Value, Total	$ 21,883	$ 30,848