Investments (Schedule of Contractual Maturities of Fixed Maturity Investments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost, Due in less than one year	$ 119,010
Trading Debt Securities, Amortized Cost, Due after one through five years	2,951,583
Trading Debt Securities, Amortized Cost, Due after five through ten years	499,093
Trading Debt Securities, Amortized Cost, Due after ten years	81,215
Trading Debt Securities, Amortized Cost	4,532,381
Trading Debt Securities, Fair Value, Due in less than one year	119,599
Trading Debt Securities, Fair Value, Due after one through five years	2,963,494
Trading Debt Securities, Fair Value, Due after five through ten years	504,919
Trading Debt Securities, Fair Value, Due after ten years	100,732
Trading Debt Securities, Fair Value	4,587,412
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	26,402	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	30,205	34,241
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost, Due in less than one year	119,010
Debt Securities, Amortized Cost, Due after one through five years	2,951,583
Debt Securities, Amortized Cost, Due after five through ten years	499,093
Debt Securities, Amortized Cost, Due after ten years	81,215
Debt Securities, Amortized Cost	4,558,783
Debt Securities, Fair Value, Due in less than one year	119,599
Debt Securities, Fair Value, Due after one through give years	2,963,494
Debt Securities, Fair Value, Due after five through ten years	504,919
Debt Securities, Fair Value, Due after ten years	100,732
Debt Securities, Fair Value	4,617,617
Mortgage-backed
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost	866,984
Trading Debt Securities, Fair Value	883,896
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost	22,912
Available for Sale, Fair Value	26,514
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost	889,896
Debt Securities, Fair Value	910,410
Asset-backed
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost	14,496
Trading Debt Securities, Fair Value	14,772
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost	3,490
Available for Sale, Fair Value	3,691
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost	17,986
Debt Securities, Fair Value	$ 18,463

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