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	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	$ 60,202	$ 217,587
Total fixed-maturity securities, Gross Unrealized Gains	590	1,730
Total fixed-maturity securities, Gross Unrealized Losses	(151)	(516)
Total fixed-maturity securities, Estimated Fair Value	60,641	218,801
Total fixed-maturity securities held in trust, Amortized Cost	52,307	144,909
Total fixed-maturity securities held in trust, Gross Unrealized Gains	411	1,498
Total fixed-maturity securities held in trust, Gross Unrealized Losses	(140)	(503)
Total fixed-maturity securities held in trust, Estimated Fair Value	52,578	145,904
Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less total unrestricted fixed-maturity securities, Amortized Cost	7,895	7,326
Less total unrestricted fixed-maturity securities, Gross Unrealized Gains	179	232
Less total unrestricted fixed-maturity securities, Gross Unrealized Losses	(11)	(13)
Less total unrestricted fixed-maturity securities, Estimated Fair Value	8,063	7,545
Held to Maturity [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less total unrestricted fixed-maturity securities, Amortized Cost		65,352
Less total unrestricted fixed-maturity securities, Estimated Fair Value		65,352
Obligations of U.S. Government Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	6,491	15,868
Total fixed-maturity securities, Gross Unrealized Gains	12	127
Total fixed-maturity securities, Gross Unrealized Losses	(28)	(163)
Total fixed-maturity securities, Estimated Fair Value	6,475	15,832
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	41,018	80,624
Total fixed-maturity securities, Gross Unrealized Gains	531	1,450
Total fixed-maturity securities, Gross Unrealized Losses	(65)	(182)
Total fixed-maturity securities, Estimated Fair Value	41,484	81,892
Foreign Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	12,693	22,166
Total fixed-maturity securities, Gross Unrealized Gains	47	149
Total fixed-maturity securities, Gross Unrealized Losses	(58)	(170)
Total fixed-maturity securities, Estimated Fair Value	12,682	22,145
Commercial Paper [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost		98,929
Total fixed-maturity securities, Gross Unrealized Gains		4
Total fixed-maturity securities, Gross Unrealized Losses		(1)
Total fixed-maturity securities, Estimated Fair Value		$ 98,932