Derivative Instruments (Total Unrealized and Realized Gains (Losses) recorded in the Consolidated Income Statement) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (15,755)		$ (20,410)
Investment Portfolio [Member] | Net Realized Investment Gains [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	723		723
Investment Portfolio [Member] | Net Realized Investment Losses [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Futures [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(10,763)		(16,259)
Investment Portfolio [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(10,040)		(15,536)
Operating Activities [Member] | Foreign Exchange Gains (Losses) [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	1,345	(1,361)	2,601	(1,412)
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (8,695)	$ (1,361)	$ (12,935)	$ (1,412)