Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Available for Sale Amortized Cost
Due in one year or less	$ 1,021,139
Due after one year through five years	1,387,097
Due after five years through ten years	568,879
Due after ten years	460,227
Total	4,386,806	4,838,695
Available for Sale Securities Fair Value
Due in one year or less	1,065,026
Due after one year through five years	1,507,584
Due after five years through ten years	651,200
Due after ten years	553,902
Total	4,778,391	5,273,767
Residential Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	350,862
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	366,894
Commercial Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	418,297
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	445,795
Asset-backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	180,305
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	$ 187,990

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

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