Net Investment Income (Net Investment Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Gross investment income	$ 529,820	$ 534,085	$ 382,596
Investment expense	(3,469)	(3,560)	(3,588)
Net investment income	526,351	530,525	379,008
Fixed maturity securities, including cash and cash equivalents and loans receivable [Member]
Gross investment income	483,905	501,750	495,140
Equity Securities available for sale [Member]
Gross investment income	12,416	11,661	20,295
Investment funds [Member]
Gross investment income	9,452	(6,481)	(163,862)
Arbitrage trading account [Member]
Gross investment income	16,576	27,155	31,023
Real Estate [Domain]
Gross investment income	$ 7,471	$ 0	$ 0