Investment Securities - Schedule of Investments in Accordance with Fair Value Measurement (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Class of Securities:
Total fixed-maturity securities	$ 119,999	$ 60,641
Total investments fair value	131,291	149,492
Level 1
Class of Securities:
Total fixed-maturity securities	87,121	20,770
Total investments fair value	98,413	109,621
Level 2
Class of Securities:
Total fixed-maturity securities	32,878	39,871
Total investments fair value	32,878	39,871
Obligations of U.S. Government Sponsored Enterprises [Member]
Class of Securities:
Total fixed-maturity securities	75,464	6,475
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 1
Class of Securities:
Total fixed-maturity securities	71,979	3,009
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 2
Class of Securities:
Total fixed-maturity securities	3,485	3,466
Corporate Debt Securities [Member]
Class of Securities:
Total fixed-maturity securities	28,587	41,484
Corporate Debt Securities [Member] | Level 1
Class of Securities:
Total fixed-maturity securities	9,071	14,939
Corporate Debt Securities [Member] | Level 2
Class of Securities:
Total fixed-maturity securities	19,516	26,545
Commercial Paper [Member]
Class of Securities:
Total fixed-maturity securities	4,999
Commercial Paper [Member] | Level 1
Class of Securities:
Total fixed-maturity securities	4,999
Foreign Corporate Debt Securities [Member]
Class of Securities:
Total fixed-maturity securities	10,949	12,682
Foreign Corporate Debt Securities [Member] | Level 1
Class of Securities:
Total fixed-maturity securities	1,072	2,822
Foreign Corporate Debt Securities [Member] | Level 2
Class of Securities:
Total fixed-maturity securities	9,877	9,860
Money Market Funds [Member]
Class of Securities:
Total investments fair value	11,292	88,851
Money Market Funds [Member] | Level 1
Class of Securities:
Total investments fair value	$ 11,292	$ 88,851