Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Available for Sale Amortized Cost
Due in one year or less	$ 890,150
Due after one year through five years	797,842
Due after five years through ten years	580,012
Due after ten years	469,516
Total	3,491,116	3,827,496
Available for Sale Securities Fair Value
Due in one year or less	913,772
Due after one year through five years	872,407
Due after five years through ten years	634,099
Due after ten years	506,578
Total	3,704,512	4,203,450
Residential Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	199,390
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	205,130
Commercial Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	371,503
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	381,575
Asset-backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	182,703
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	$ 190,951

Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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