Investment Funds Investment Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2011	Jun. 30, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Carrying Value	$ 728,505			$ 728,505	$ 680,638
Income (Losses) from Investment Funds	162,691	150,158	297,137	321,409
Real Estate Funds [Member]
Investment Holdings [Line Items]
Carrying Value	381,907			381,907	373,413
Energy Fund [Member]
Investment Holdings [Line Items]
Carrying Value	140,802			140,802	98,974
Arbitrage [Member]
Investment Holdings [Line Items]
Carrying Value	57,346			57,346	58,008
Other [Member]
Investment Holdings [Line Items]
Carrying Value	148,450			148,450	150,243
Investment Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			31,889	63,242
Investment Funds [Member] | Real Estate Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			10,647	11,290
Investment Funds [Member] | Energy Fund [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			23,133	49,780
Investment Funds [Member] | Arbitrage [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			354	(662)
Investment Funds [Member] | Other [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds			$ (2,245)	$ 2,834