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	Sep. 30, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	$ 275,845	$ 298,978
Total fixed-maturity securities, Gross Unrealized Gains	5,777	6,442
Total fixed-maturity securities, Gross Unrealized Losses	(328)	(1,375)
Total fixed-maturity securities, Estimated Fair Value	281,294	304,045
Less total unrestricted fixed-maturity securities Amortized Cost	72,690	5,348
Less total unrestricted fixed-maturity securities, Gross unrealized gains	232	151
Less total unrestricted fixed-maturity securities, Gross unrealized losses	(140)	(9)
Less total unrestricted fixed-maturity securities, Estimated Fair Value	72,782	5,490
Total fixed-maturity securities held in trust, Amortized Cost	203,155	293,630
Total fixed-maturity securities held in trust, Gross Unrealized Gains	5,545	6,291
Total fixed-maturity securities held in trust, Gross Unrealized Losses	(188)	(1,366)
Total fixed-maturity securities held in trust, Estimated Fair Value	208,512	298,555
US Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	250	250
Total fixed-maturity securities, Estimated Fair Value	250	250
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	101,400	122,874
Total fixed-maturity securities, Gross Unrealized Gains	1,608	2,029
Total fixed-maturity securities, Gross Unrealized Losses	(100)	(267)
Total fixed-maturity securities, Estimated Fair Value	102,908	124,636
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	99,416	129,916
Total fixed-maturity securities, Gross Unrealized Gains	3,611	3,791
Total fixed-maturity securities, Gross Unrealized Losses	(151)	(845)
Total fixed-maturity securities, Estimated Fair Value	102,876	132,862
Foreign Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	18,342	26,800
Total fixed-maturity securities, Gross Unrealized Gains	447	546
Total fixed-maturity securities, Gross Unrealized Losses	(5)	(117)
Total fixed-maturity securities, Estimated Fair Value	18,784	27,229
Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	11,571	19,138
Total fixed-maturity securities, Gross Unrealized Gains	55	76
Total fixed-maturity securities, Gross Unrealized Losses	(65)	(146)
Total fixed-maturity securities, Estimated Fair Value	11,561	19,068
Commercial Paper [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity securities amortized cost	44,866
Total fixed-maturity securities, Gross Unrealized Gains	56
Total fixed-maturity securities, Gross Unrealized Losses	(7)
Total fixed-maturity securities, Estimated Fair Value	$ 44,915