Investment Funds Investment Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investment Holdings [Line Items]
Carrying Value	$ 793,603		$ 809,689
Income (Losses) from Investment Funds	137,941	158,718
Real Estate Funds [Member]
Investment Holdings [Line Items]
Carrying Value	379,006		373,259
Energy Fund [Member]
Investment Holdings [Line Items]
Carrying Value	147,383		146,325
Arbitrage [Member]
Investment Holdings [Line Items]
Carrying Value	63,462		63,920
Other [Member]
Investment Holdings [Line Items]
Carrying Value	203,752		226,185
Investment Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	10,934	27,623
Investment Funds [Member] | Real Estate Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	(2,001)	8,655
Investment Funds [Member] | Energy Fund [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	9,466	17,938
Investment Funds [Member] | Arbitrage [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	(458)	1,770
Investment Funds [Member] | Other [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	$ 3,927	$ (740)