Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Amortized Cost, 2017	$ 58,544
Amortized Cost, 2018	15,338
Amortized Cost, 2019	3,030
Total fixed-maturity securities, Amortized Cost	76,912	$ 99,088
Estimated Fair Value, 2017	58,546
Estimated Fair Value, 2018	15,280
Estimated Fair Value, 2019	3,005
Total fixed-maturity securities, Estimated Fair Value	$ 76,831	$ 99,055