Investment Funds Investment Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Investment Holdings [Line Items]
Carrying Value	$ 679,689		$ 680,638
Income (Losses) from Investment Funds	158,718	146,979
Real Estate Funds [Member]
Investment Holdings [Line Items]
Carrying Value	377,854		373,413
Energy Fund [Member]
Investment Holdings [Line Items]
Carrying Value	110,330		98,974
Arbitrage [Member]
Investment Holdings [Line Items]
Carrying Value	59,778		58,008
Other [Member]
Investment Holdings [Line Items]
Carrying Value	131,727		150,243
Investment Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	27,623	16,387
Investment Funds [Member] | Real Estate Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	8,655	3,492
Investment Funds [Member] | Energy Fund [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	17,938	13,359
Investment Funds [Member] | Arbitrage [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	1,770	1,880
Investment Funds [Member] | Other [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	$ (740)	$ (2,344)