Investments (Schedule of Realized Gains and Losses) (Details) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Investments
Gross realized gains on sale of securities	$ 34,611	$ 78,572	$ 78,168	$ 130,239
Gross realized losses on sale of securities	(3,330)	(6,724)	(25,262)	(13,130)
Treasury yield hedge		(3,958)		(3,958)
Futures not designated as hedges	(15,755)		(20,410)
Foreign exchange forwards not designated as hedges	(560)		(560)
Mark-to-market changes: debt securities trading	31,872	32,746	45,336	60,477
Mark-to-market changes: foreign exchange forwards and futures not designated as hedges	6,275		5,434
Mark-to-market changes: hedge funds and equity securities	5,765	(5,703)	26,548	(1,208)
Net realized investment gains	58,878	94,933	109,254	172,420
Proceeds from sale of available for sale securities	202,671	1,306,625	546,191	1,846,074
Proceeds from sale of trading securities	$ 1,432,148	$ 1,215,553	$ 3,418,548	$ 5,297,353

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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