Investment Securities - Schedule of Investments in Accordance with Fair Value Measurement (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Class of Security:
Total fixed maturity securities	$ 270,604	$ 281,547
Total investments fair value	290,388	311,097
Obligations of U.S. Government Sponsored Enterprises [Member]
Class of Security:
Total fixed maturity securities	71,750	98,363
Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities	103,607	94,974
Commercial Paper [Member]
Class of Security:
Total fixed maturity securities	62,990	54,948
Foreign Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities	28,856	18,666
Commercial Mortgage-Backed Securities [Member]
Class of Security:
Total fixed maturity securities	3,401	10,518
Money Market Funds [Member]
Class of Security:
Total investments fair value	19,784	33,628
Fair Value, Inputs, Level 1 [Member]
Class of Security:
Total fixed maturity securities	97,040	90,144
Total investments fair value	116,824	123,772
Fair Value, Inputs, Level 1 [Member] | Obligations of U.S. Government Sponsored Enterprises [Member]
Class of Security:
Total fixed maturity securities	11,211	11,362
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities	21,302	22,833
Fair Value, Inputs, Level 1 [Member] | Commercial Paper [Member]
Class of Security:
Total fixed maturity securities	62,990	54,948
Fair Value, Inputs, Level 1 [Member] | Foreign Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities	1,537	1,001
Fair Value, Inputs, Level 1 [Member] | Commercial Mortgage-Backed Securities [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Class of Security:
Total investments fair value	19,784	33,628
Fair Value, Inputs, Level 2 [Member]
Class of Security:
Total fixed maturity securities	173,564	187,325
Total investments fair value	173,564	187,325
Fair Value, Inputs, Level 2 [Member] | Obligations of U.S. Government Sponsored Enterprises [Member]
Class of Security:
Total fixed maturity securities	60,539	87,001
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities	82,305	72,141
Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 2 [Member] | Foreign Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities	27,319	17,665
Fair Value, Inputs, Level 2 [Member] | Commercial Mortgage-Backed Securities [Member]
Class of Security:
Total fixed maturity securities	3,401	10,518
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Class of Security:
Total investments fair value
Fair Value, Inputs, Level 3 [Member]
Class of Security:
Total fixed maturity securities
Total investments fair value
Fair Value, Inputs, Level 3 [Member] | Obligations of U.S. Government Sponsored Enterprises [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 3 [Member] | Commercial Paper [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 3 [Member] | Foreign Corporate Debt Securities [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 3 [Member] | Commercial Mortgage-Backed Securities [Member]
Class of Security:
Total fixed maturity securities
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Class of Security:
Total investments fair value