Derivative Investments (Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012		Mar. 31, 2012
Derivatives, Fair Value [Line Items]
Derivatives, index options	$ 130,967	$ 57,890	$ 130,967		$ 57,890
Liability Derivatives			149,895	[1]	72,470	[1]
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivatives, index options	130,967				57,890
Liability Derivatives	149,895				72,470
Derivatives Not Designated as Hedging Instruments [Member] | Equity Index Options [Member] | Derivatives, Index Options [Member]
Derivatives, Fair Value [Line Items]
Derivatives, index options	130,967				57,890
Derivatives Not Designated as Hedging Instruments [Member] | Fixed-Index Products [Member] | Universal Life and Annuity Contracts [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 149,895				$ 72,470

[1] Represents the fair value of certain product-related embedded derivatives that were recorded at fair value.