Derivative Instruments (Details) - Earnings relating to derivative instruments not formally designated as hedging instruments (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments Gain Loss [Line Items]
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	$ (4,585)	$ (1,875)	$ (13,675)
Net realized and unrealized gains (losses) on derivative instruments	5,221	(10,738)	(33,843)
Not Designated as Hedging Instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Total derivatives not designated as hedging instruments	9,806	(8,863)	(20,168)
Investment Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Interest rate exposure	4,394	(1,021)	3,511
Foreign exchange exposure	(1,084)	(302)	(15,642)
Credit exposure	(7,611)	(16,527)	(6,315)
Financial market exposure	3,073	(5,131)	2,125
Financial Operations Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Credit exposure	10,511	16,976	(7,281)
Other Non Investment Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Contingent capital facility	0	(6,068)	(8,233)
Guaranteed minimum income benefit contract	(2,906)	(1,300)	1,719
Modified coinsurance funds withheld contract	$ 3,429	$ 4,510	$ 9,948