Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Estimated Fair Values of Fixed-Maturity Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	$ 119,635	$ 60,202
Total fixed-maturity securities, Gross Unrealized Gains	395	590
Total fixed-maturity securities, Gross Unrealized Losses	(31)	(151)
Total fixed-maturity securities, Estimated Fair Value	119,999	60,641
Less total unrestricted fixed-maturity securities, Amortized Cost	74,041	7,895
Less total unrestricted fixed-maturity securities, Gross Unrealized Gains	147	179
Less total unrestricted fixed-maturity securities, Gross Unrealized Losses	(5)	(11)
Less total unrestricted fixed-maturity securities, Estimated Fair Value	74,183	8,063
Total fixed-maturity securities held in trust, Amortized Cost	45,594	52,307
Total fixed-maturity securities held in trust, Gross Unrealized Gains	248	411
Total fixed-maturity securities held in trust, Gross Unrealized Losses	(26)	(140)
Total fixed-maturity securities held in trust, Estimated Fair Value	45,816	52,578
Obligations of U.S. Government Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	75,474	6,491
Total fixed-maturity securities, Gross Unrealized Gains	6	12
Total fixed-maturity securities, Gross Unrealized Losses	(16)	(28)
Total fixed-maturity securities, Estimated Fair Value	75,464	6,475
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	28,264	41,018
Total fixed-maturity securities, Gross Unrealized Gains	331	531
Total fixed-maturity securities, Gross Unrealized Losses	(8)	(65)
Total fixed-maturity securities, Estimated Fair Value	28,587	41,484
Foreign Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	10,899	12,693
Total fixed-maturity securities, Gross Unrealized Gains	57	47
Total fixed-maturity securities, Gross Unrealized Losses	(7)	(58)
Total fixed-maturity securities, Estimated Fair Value	10,949	12,682
Commercial Paper [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	4,998
Total fixed-maturity securities, Gross Unrealized Gains	1
Total fixed-maturity securities, Estimated Fair Value	$ 4,999