Investments - Amortized Cost and Fair Value of Fixed Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 3,086	$ 16,934
Due after one year through five years	20,221	13,876
Due after five years	233	232
Amortized Cost, Total	23,540	31,042
Fair Value
Due in one year or less	3,075	16,899
Due after one year through five years	19,859	13,708
Due after five years	233	241
Fair Value, Total	$ 23,167	$ 30,848