Investments (Schedule of Contractual Maturities of Fixed Maturity Investments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost, Due in less than one year	$ 97,830
Trading Debt Securities, Amortized Cost, Due after one through five years	2,951,631
Trading Debt Securities, Amortized Cost, Due after five through ten years	595,874
Trading Debt Securities, Amortized Cost, Due after ten years	108,080
Trading Debt Securities, Amortized Cost	4,735,061
Trading Debt Securities, Fair Value, Due in less than one year	97,868
Trading Debt Securities, Fair Value, Due after one through five years	2,949,329
Trading Debt Securities, Fair Value, Due after five through ten years	593,633
Trading Debt Securities, Fair Value, Due after ten years	111,174
Trading Debt Securities, Fair Value	4,750,766
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	24,664	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	28,069	34,241
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost, Due in less than one year	97,830
Debt Securities, Amortized Cost, Due after one through five years	2,951,631
Debt Securities, Amortized Cost, Due after five through ten years	595,874
Debt Securities, Amortized Cost, Due after ten years	108,080
Debt Securities, Amortized Cost	4,759,725
Debt Securities, Fair Value, Due in less than one year	97,868
Debt Securities, Fair Value, Due after one through give years	2,949,329
Debt Securities, Fair Value, Due after five through ten years	593,633
Debt Securities, Fair Value, Due after ten years	111,174
Debt Securities, Fair Value	4,778,835
Mortgage-backed
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost	953,480
Trading Debt Securities, Fair Value	970,510
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost	21,467
Available for Sale, Fair Value	24,718
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost	974,947
Debt Securities, Fair Value	995,228
Asset-backed
Trading Securities [Abstract]
Trading Debt Securities, Amortized Cost	28,166
Trading Debt Securities, Fair Value	28,252
Available-for-sale Securities [Abstract]
Available for Sale, Amortized Cost	3,197
Available for Sale, Fair Value	3,351
Fixed Maturity Investments [Abstract]
Debt Securities, Amortized Cost	31,363
Debt Securities, Fair Value	$ 31,603

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