Derivative Instruments (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Derivative Instruments
Notional Amount	$ 4,466,308	$ 3,735,835
Carrying Value / Fair Value of Assets	176,939	110,360
Carrying Value / Fair Value of Liabilities	1,078,983	1,060,435
Designated As Hedging Member
Derivative Instruments
Notional Amount	637,106	637,106
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	68,409	47,467
Designated As Hedging Member | Interest Rate Swap Member
Derivative Instruments
Notional Amount	21,783	21,783
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	1,984	1,718
Designated As Hedging Member | Currency Swap Member
Derivative Instruments
Notional Amount	615,323	615,323
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	66,425	45,749
Designated As Non Hedging Member
Derivative Instruments
Notional Amount	3,829,202	3,098,729
Carrying Value / Fair Value of Assets	176,939	110,360
Carrying Value / Fair Value of Liabilities	1,010,574	1,012,968
Designated As Non Hedging Member | Interest Rate Swap Member
Derivative Instruments
Notional Amount	2,623,012	2,302,853
Carrying Value / Fair Value of Assets	37,001	20,042
Carrying Value / Fair Value of Liabilities	29,041	17,132
Designated As Non Hedging Member | Future Member
Derivative Instruments
Notional Amount	174,096	210,295
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	0	0
Designated As Non Hedging Member | Foreign Exchange Forward Member
Derivative Instruments
Notional Amount	39,700	39,700
Carrying Value / Fair Value of Assets	5,706	5,924
Carrying Value / Fair Value of Liabilities	0	0
Designated As Non Hedging Member | Consumer Price Index Swap Member
Derivative Instruments
Notional Amount	126,091	120,340
Carrying Value / Fair Value of Assets	1,667	1,491
Carrying Value / Fair Value of Liabilities	0	0
Designated As Non Hedging Member | Credit Default Swap Member
Derivative Instruments
Notional Amount	612,500	392,500
Carrying Value / Fair Value of Assets	2,210	2,429
Carrying Value / Fair Value of Liabilities	4,201	131
Designated As Non Hedging Member | Equity Member
Derivative Instruments
Notional Amount	253,803	33,041
Carrying Value / Fair Value of Assets	44,326	5,043
Carrying Value / Fair Value of Liabilities	0	0
Designated As Non Hedging Member | Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements Member
Derivative Instruments
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	173,160	274,220
Designated As Non Hedging Member | Embedded Derivatives In Indexed Annuity Member
Derivative Instruments
Notional Amount	0	0
Carrying Value / Fair Value of Assets	86,029	75,431
Carrying Value / Fair Value of Liabilities	758,431	668,951
Designated As Non Hedging Member | Embedded Derivatives In Variable Annuity Member
Derivative Instruments
Notional Amount	0	0
Carrying Value / Fair Value of Assets	0	0
Carrying Value / Fair Value of Liabilities	$ 45,741	$ 52,534