Investments of Operating Entities and Consolidated Funds - Other Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Other investments	$ 70,151	$ 59,943
Operating Entities [Member]
Investment Holdings [Line Items]
Other investments	70,151	59,943
Operating Entities [Member] | Portfolio Funds [Member]
Investment Holdings [Line Items]
Other investments	47,287	40,350
Operating Entities [Member] | Real Estate Investments [Member]
Investment Holdings [Line Items]
Other investments	2,102	2,353
Operating Entities [Member] | Equity Method Investments [Member]
Investment Holdings [Line Items]
Other investments	20,001	16,687
Operating Entities [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Other investments	761	553
Consolidated Funds [Member]
Investment Holdings [Line Items]
Other investments	205,095	228,820
Consolidated Funds [Member] | Portfolio Funds [Member]
Investment Holdings [Line Items]
Other investments	198,235	221,480
Consolidated Funds [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Other investments	$ 6,860	$ 7,340