Investments of Operating Entities and Consolidated Funds Unrealized gains (losses) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Realized Investment Gains (Losses) on Investments, Consolidated Funds	$ (8,121)	$ 4,959	$ 16,696
Unrealized Gain (Loss) on Investments, Consolidated Funds	14,497	(34)	16,420
Realized Gain (Loss) on Derivatives, Consolidated Funds	915	(651)	(1,892)
Unrealized Gains (Losses) on Derivatives, Consolidated Funds	$ (38)	$ 68	$ 1,131