Investments - Summary of Contractual Maturities of Company's Fixed Maturity and Short-Term Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
One year or less, Amortized Cost	$ 45,814
More than one year through two years, Amortized Cost	68,066
More than two years through five years, Amortized Cost	115,824
More than five years through ten years, Amortized Cost	37,189
More than ten years, Amortized cost	36,572
Total amortized cost	308,790	$ 244,110
One year or less, Fair Value	43,567
More than one year through two years, Fair Value	66,565
More than two years through five years, Fair Value	112,928
More than five years through ten years, Fair Value	36,895
More than ten years, Fair Value	36,981
Total fair value	$ 302,301
One year or less, Percentage of Total Fair Value	14.40%
More than one year through two years, Percentage of Total Fair Value	22.00%
More than two years through five years, Percentage of Total Fair Value	37.40%
More than five years through ten years, Percentage of Total Fair Value	12.20%
More than ten years, Percentage of Total Fair Value	12.20%
Percentage of Total Fair Value	100.00%
Residential Mortgage-Backed
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 665	3,305
Total fair value	$ 715
Percentage of Total Fair Value	0.20%
Asset-Backed
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 4,660	$ 41,980
Total fair value	$ 4,650
Percentage of Total Fair Value	1.60%