Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Amortized Cost, 2017	$ 9,027
Amortized Cost, 2018	14,299
Amortized Cost, 2019	789
Total fixed-maturity securities, Amortized Cost	24,115	$ 76,912
Estimated Fair Value, 2017	9,025
Estimated Fair Value, 2018	14,248
Estimated Fair Value, 2019	789
Total fixed-maturity securities, Estimated Fair Value	$ 24,062	$ 76,831