Investments - Summary of Contractual Maturities of Company's Fixed Maturity and Short-Term Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
One year or less, Amortized Cost	$ 56,628
More than one year through two years, Amortized Cost	65,181
More than two years through five years, Amortized Cost	88,747
More than five years through ten years, Amortized Cost	38,113
More than ten years, Amortized cost	36,159
Total amortized cost	290,034	$ 308,790
One year or less, Fair Value	55,194
More than one year through two years, Fair Value	64,237
More than two years through five years, Fair Value	88,172
More than five years through ten years, Fair Value	39,088
More than ten years, Fair Value	38,525
Total fair value	$ 290,487
One year or less, Percentage of Total Fair Value	19.00%
More than one year through two years, Percentage of Total Fair Value	22.10%
More than two years through five years, Percentage of Total Fair Value	30.30%
More than five years through ten years, Percentage of Total Fair Value	13.50%
More than ten years, Percentage of Total Fair Value	13.30%
Percentage of Total Fair Value	100.00%
Residential Mortgage-Backed
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 590	665
Total fair value	$ 641
Percentage of Total Fair Value	0.20%
Asset-Backed
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 4,616	$ 4,660
Total fair value	$ 4,630
Percentage of Total Fair Value	1.60%