Investments - Amortized Cost and Fair Values of Fixed Maturity and Short-Term Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 299,733	$ 308,790
Gross Unrealized Gains	6,701	1,217
Gross Unrealized Losses Non-OTTI	(4,104)	(7,706)
Fair Value	302,330	302,301
U.S. government and agency
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,364	25,102
Gross Unrealized Gains	164	80
Gross Unrealized Losses Non-OTTI	0	(341)
Fair Value	13,528	24,841
Non-U.S. government
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	89,836	89,631
Gross Unrealized Gains	2,530	42
Gross Unrealized Losses Non-OTTI	(2,159)	(3,889)
Fair Value	90,207	85,784
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	184,886	182,773
Gross Unrealized Gains	3,820	1,040
Gross Unrealized Losses Non-OTTI	(1,945)	(3,429)
Fair Value	186,761	180,384
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,500	5,959
Gross Unrealized Gains	102	4
Gross Unrealized Losses Non-OTTI	0	(36)
Fair Value	6,602	5,927
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	569	665
Gross Unrealized Gains	55	51
Gross Unrealized Losses Non-OTTI	0	(1)
Fair Value	624	715
Asset-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,578	4,660
Gross Unrealized Gains	30	0
Gross Unrealized Losses Non-OTTI	0	(10)
Fair Value	$ 4,608	$ 4,650