Derivative Instruments (Details) - Earnings relating to derivative instruments not formally designated as hedging instruments (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments Gain Loss [Line Items]
Total derivatives not designated as hedging instruments	$ 6,451	$ (25,874)	$ 7,486	$ (33,521)
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	(197)	(1,042)	(4,830)	(778)
Net realized and unrealized gains (losses) on derivative instruments	6,254	(26,916)	2,656	(34,299)
Investment Related Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Interest rate exposure	243	2,559	860	(1,720)
Foreign exchange exposure	1,218	(23,214)	1,547	(5,763)
Credit exposure	(2,281)	5,207	343	(8,452)
Financial market exposure	2,337	(7,304)	312	(6,339)
Financial Operations Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Credit exposure	0	25	143	331
Other Non Investment Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Contingent capital facility	0	(2,075)	0	(6,158)
Guaranteed minimum income benefit contract	885	(2,038)	1,971	(860)
Modified coinsurance funds withheld contract	$ 4,049	$ 966	$ 2,310	$ (4,560)