Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Fixed income securities, amortized cost	$ 4,514,878	$ 5,927,254
Fixed income securities pledged as collateral, amortized cost	64,378	126,196
Short-term investments, amortized cost	360,069	271,118
Other investments	$ 336,013us-gaap_OtherInvestments	$ 240,969us-gaap_OtherInvestments
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000us-gaap_PreferredStockSharesAuthorized	20,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000us-gaap_CommonStockSharesAuthorized	130,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	45,005,932us-gaap_CommonStockSharesIssued	45,003,461us-gaap_CommonStockSharesIssued
Common stock, shares outstanding	45,005,932us-gaap_CommonStockSharesOutstanding	45,003,461us-gaap_CommonStockSharesOutstanding
Treasury stock, shares	2,459us-gaap_TreasuryStockShares	937us-gaap_TreasuryStockShares

Amortized cost basis of available for sale securities that serve as collateral for borrowings.

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This item represents the amortized cost of other short term investments not otherwise specified in the taxonomy that will be realized in a short period of time, usually less than one year, net of adjustments made for accretion, amortization, other-than-temporary impairments.

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

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Other investments not otherwise specified in the taxonomy.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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