Investment Securities - Schedule of Investments in Accordance with Fair Value Measurement (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Class of Security:
Total fixed maturity securities	$ 281,547	$ 277,469
Total investments fair value	306,621	311,097
Obligations of U.S. government sponsored enterprises [Member]
Class of Security:
Total fixed maturity securities	73,896	98,363
Corporate debt securities [Member]
Class of Security:
Total fixed maturity securities	108,114	94,974
Commercial paper [Member]
Class of Security:
Total fixed maturity securities	69,607	54,948
Foreign corporate debt securities [Member]
Class of Security:
Total fixed maturity securities	21,082	18,666
Commercial Mortgage-backed securities [Member]
Class of Security:
Total fixed maturity securities	8,848	10,518
Money market funds [Member]
Class of Security:
Total investments fair value	25,074	33,628
Fair Value, Inputs, Level 1 [Member]
Class of Security:
Total fixed maturity securities	107,700	90,144
Total investments fair value	132,774	123,772
Fair Value, Inputs, Level 1 [Member] \| Obligations of U.S. government sponsored enterprises [Member]
Class of Security:
Total fixed maturity securities	11,305	11,362
Fair Value, Inputs, Level 1 [Member] \| Corporate debt securities [Member]
Class of Security:
Total fixed maturity securities	25,236	22,833
Fair Value, Inputs, Level 1 [Member] \| Commercial paper [Member]
Class of Security:
Total fixed maturity securities	69,607	54,948
Fair Value, Inputs, Level 1 [Member] \| Foreign corporate debt securities [Member]
Class of Security:
Total fixed maturity securities	1,552	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	25,074	33,628
Fair Value, Inputs, Level 2 [Member]
Class of Security:
Total fixed maturity securities	173,847	187,325
Total investments fair value	173,847	187,325
Fair Value, Inputs, Level 2 [Member] \| Obligations of U.S. government sponsored enterprises [Member]
Class of Security:
Total fixed maturity securities	62,591	87,001
Fair Value, Inputs, Level 2 [Member] \| Corporate debt securities [Member]
Class of Security:
Total fixed maturity securities	82,878	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	19,530	17,665
Fair Value, Inputs, Level 2 [Member] \| Commercial Mortgage-backed securities [Member]
Class of Security:
Total fixed maturity securities	8,848	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

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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