Investment Funds Investment Funds (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Investment funds	$ 858,394		$ 809,689
Income (Losses) from Investment Funds	33,510	63,242
Real estate
Schedule of Equity Method Investments [Line Items]
Investment funds	381,855		373,259
Income (Losses) from Investment Funds	1,260	11,290
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds	146,966		146,325
Income (Losses) from Investment Funds	25,199	49,780
Arbitrage
Schedule of Equity Method Investments [Line Items]
Investment funds	65,651		63,920
Income (Losses) from Investment Funds	1,731	(662)
Other
Schedule of Equity Method Investments [Line Items]
Investment funds	263,922		226,185
Income (Losses) from Investment Funds	$ 5,320	$ 2,834