Derivative Instruments (Details) - Earnings relating to derivative instruments not formally designated as hedging instruments (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative Instruments Gain Loss [Line Items]
Total derivatives not designated as hedging instruments	$ (2,106)	$ (9,993)	$ 1,035	$ (7,647)
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	(2,194)	(957)	(4,633)	264
Net realized and unrealized gains (losses) on derivative instruments	(4,300)	(10,950)	(3,598)	(7,383)
Investment Related Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Interest rate exposure	(83)	(4,319)	617	(4,151)
Foreign exchange exposure	683	11,014	329	17,451
Credit exposure	6,323	(12,693)	2,624	(13,659)
Financial market exposure	(5,969)	(32)	(2,025)	837
Financial Operations Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Credit exposure	0	124	143	306
Other Non Investment Derivatives [Member]
Derivative Instruments Gain Loss [Line Items]
Contingent capital facility	0	(2,053)	0	(4,083)
Guaranteed minimum income benefit contract	(929)	(1,130)	1,086	1,179
Modified coinsurance funds withheld contract	$ (2,131)	$ (904)	$ (1,739)	$ (5,527)