Derivative Instruments (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ 254,136,000	$ (36,056,000)	$ 212,030,000
Policy Acquisition Costs And Other Insurance Expenses	1,306,470,000	990,021,000	1,137,589,000
Interest credited	379,915,000	316,394,000	309,982,000
Interest Rate Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	16,028,000	178,338,000	68,736,000
Future [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(20,245,000)	(945,000)	(44,959,000)
Foreign Exchange Forward [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(5,644,000)	1,675,000	3,387,000
Consumer Price Index Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(267,000)	1,821,000	962,000
Credit Default Swap [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	18,359,000	(63,000)	4,786,000
Equity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	(69,677,000)	7,818,000	(3,006,000)
Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	115,009,000	(87,236,000)	160,274,000
Embedded Derivatives In Indexed Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Policy Acquisition Costs And Other Insurance Expenses	(630,000)	(24,551,000)	6,457,000
Interest credited	(29,804,000)	(90,370,000)	(51,445,000)
Embedded Derivatives In Variable Annuity [Member]
Income Affect Of Non Hedging Derivatives [Line Items]
Total investment related gains (losses), net	$ 104,613,000	$ (224,184,000)	$ (28,786,000)