Investments - Contractual Maturities of Fixed Maturity and Short-Term Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
One year or less	$ 51,327
More than one year through two years	68,189
More than two years through five years	87,040
More than five years through ten years	41,192
More than ten years	46,838
Amortized Cost	299,733	$ 308,790
Fair Value
One year or less	50,119
More than one year through two years	67,500
More than two years through five years	86,492
More than five years through ten years	42,841
More than ten years	50,146
Fair Value	$ 302,330	302,301
% of Total Fair Value
One year or less	16.60%
More than one year through two years	22.30%
More than two years through five years	28.60%
More than five years through ten years	14.20%
More than ten years	16.60%
Percentage of Total Fair Value	100.00%
Residential mortgage-backed
Amortized Cost
Securities without single maturity date	$ 569
Amortized Cost	569	665
Fair Value
Securities without single maturity date	624
Fair Value	$ 624	715
% of Total Fair Value
Securities without single maturity date	0.20%
Asset-backed
Amortized Cost
Securities without single maturity date	$ 4,578
Amortized Cost	4,578	4,660
Fair Value
Securities without single maturity date	4,608
Fair Value	$ 4,608	$ 4,650
% of Total Fair Value
Securities without single maturity date	1.50%