Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	$ 311,309	$ 829,577
Equity securities	6,112	11,857
Short-term investments, at fair value	611,267	76,502
Trading securities		12,712
Total	928,688	930,648
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	242,555	31,032
Equity securities		5,151
Short-term investments, at fair value	611,267	76,502
Trading securities		990
Total	853,822	113,675
Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	68,754	798,545
Equity securities	39
Short-term investments, at fair value
Trading securities		11,722
Total	68,793	810,267
Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Equity securities	6,073	6,706
Short-term investments, at fair value
Trading securities
Total	6,073	6,706
U.S. Treasury securities and other government corporations and agencies [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	256,953	56,541
U.S. Treasury securities and other government corporations and agencies [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	242,555	31,032
U.S. Treasury securities and other government corporations and agencies [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	14,398	25,509
U.S. Treasury securities and other government corporations and agencies [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
States of the U.S. and political subdivisions of the states [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	4,425	46,164
States of the U.S. and political subdivisions of the states [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
States of the U.S. and political subdivisions of the states [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	4,425	46,164
States of the U.S. and political subdivisions of the states [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Corporate securities [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	35,268	340,729
Corporate securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Corporate securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	35,268	340,729
Corporate securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Mortgage-backed securities [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	4,866	248,240
Mortgage-backed securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Mortgage-backed securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	4,866	248,240
Mortgage-backed securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Commercial mortgage-backed securities [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	2,825	63,215
Commercial mortgage-backed securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Commercial mortgage-backed securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	2,825	63,215
Commercial mortgage-backed securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Asset-backed securities [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	6,972	74,688
Asset-backed securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value
Asset-backed securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value	6,972	74,688
Asset-backed securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets measured at fair value on a recurring basis
Fixed maturity securities, at fair value

Amount of debt securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

Amount of equity securities categorized neither as held-to-maturity nor as trading.

+ References

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+ Details

- Definition

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.

+ References+ Details

- Definition

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 Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

+ References+ Details