Investments (Schedule of Contractual Maturities of Fixed Maturity Investments) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost, Due in less than one year	$ 100,250
Trading Debt Securities, Amortized Cost, Due after one through five years	3,057,740
Trading Debt Securities, Amortized Cost, Due after five through ten years	520,699
Trading Debt Securities, Amortized Cost, Due after ten years	102,944
Trading Debt Securities, Amortized Cost	4,754,480
Trading Debt Securities, Fair Value, Due in less than one year	100,765
Trading Debt Securities, Fair Value, Due after one through five years	3,080,879
Trading Debt Securities, Fair Value, Due after five through ten years	529,811
Trading Debt Securities, Fair Value, Due after ten years	132,568
Trading Debt Securities, Fair Value	4,841,609
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost, Due in less than one year	0
Available for Sale, Amortized Cost, Due after one through five years	0
Available for Sale, Amortized Cost, Due after five through ten years	0
Available for Sale, Amortized Cost, Due after ten years	0
Available for Sale, Amortized Cost	25,512	30,273
Available for Sale, Fair Value, Due in less than one year	0
Available for Sale, Fair Value, Due after one through five years	0
Available for Sale, Fair Value, Due after five through ten years	0
Available for Sale, Fair Value, Due after ten years	0
Available for Sale, Fair Value	29,219	34,241
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost, Due in less than one year	100,250
Debt Securities, Amortized Cost, Due after one through five years	3,057,740
Debt Securities, Amortized Cost, Due after five through ten years	520,699
Debt Securities, Amortized Cost, Due after ten years	102,944
Debt Securities, Amortized Cost	4,779,992
Debt Securities, Fair Value, Due in less than one year	100,765
Debt Securities, Fair Value, Due after one through give years	3,080,879
Debt Securities, Fair Value, Due after five through ten years	529,811
Debt Securities, Fair Value, Due after ten years	132,568
Debt Securities, Fair Value	4,870,828
Mortgage-backed
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost	943,257
Trading Debt Securities, Fair Value	966,244
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost	22,161
Available for Sale, Fair Value	25,688
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost	965,418
Debt Securities, Fair Value	991,932
Asset-backed
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost	29,590
Trading Debt Securities, Fair Value	31,342
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost	3,351
Available for Sale, Fair Value	3,531
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost	32,941
Debt Securities, Fair Value	$ 34,873

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