Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
One year or less, Amortized Cost	$ 19,240
More than one year through two years, Amortized Cost	8,011
More than two years through five years, Amortized Cost	67,270
More than five years through ten years, Amortized Cost	107,632
More than ten years, Amortized Cost	588,713
Amortized cost due in years, Total	790,866
One year or less, Fair Value	19,228
More than one year through two years, Fair Value	7,988
More than two years through five years, Fair Value	67,386
More than five years through ten years, Fair Value	105,642
More than ten years, Fair Value	568,827
Fair value due in years, Total	$ 769,071	$ 826,372
One year or less, Percentage of Total Fair Value	2.50%
More than one year through two years, Percentage of Total Fair Value	1.00%
More than two years through five years, Percentage of Total Fair Value	8.80%
More than five years through ten years, Percentage of Total Fair Value	13.70%
More than ten years, Percentage of Total Fair Value	74.00%
Percentage of Fair Value, Total	100.00%