Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Amortized Cost, 2017	$ 30,994
Amortized Cost, 2018	15,319
Amortized Cost, 2019	3,026
Total fixed-maturity securities, Amortized Cost	49,339	$ 76,912
Estimated Fair Value, 2017	30,991
Estimated Fair Value, 2018	15,281
Estimated Fair Value, 2019	3,008
Total fixed-maturity securities, Estimated Fair Value	$ 49,280	$ 76,831