Investments - Amortized Cost and Estimated Fair Values 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]
Amortized Cost	$ 308,790	$ 244,110
Gross Unrealized Gains	1,217	1,623
Gross Unrealized Losses Non-OTTI	(7,706)	(4,622)
Fair Value	302,301	241,111
U.S. Government and Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,102	24,167
Gross Unrealized Gains	80	182
Gross Unrealized Losses Non-OTTI	(341)	(7)
Fair Value	24,841	24,342
Non-U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	89,631	72,913
Gross Unrealized Gains	42	386
Gross Unrealized Losses Non-OTTI	(3,889)	(2,805)
Fair Value	85,784	70,494
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	182,773	101,745
Gross Unrealized Gains	1,040	964
Gross Unrealized Losses Non-OTTI	(3,429)	(1,653)
Fair Value	180,384	101,056
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,959
Gross Unrealized Gains	4
Gross Unrealized Losses Non-OTTI	(36)
Fair Value	5,927
Residential Mortgage-Backed
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	665	3,305
Gross Unrealized Gains	51	76
Gross Unrealized Losses Non-OTTI	(1)	(138)
Fair Value	715	3,243
Asset-Backed
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,660	41,980
Gross Unrealized Gains	0	15
Gross Unrealized Losses Non-OTTI	(10)	(19)
Fair Value	$ 4,650	$ 41,976