Investments of Operating Entities and Consolidated Funds - Other Investments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Other investments	$ 68,336	$ 59,943
Operating Entities [Member]
Investment Holdings [Line Items]
Other investments	68,336	59,943
Operating Entities [Member] | Portfolio Funds [Member]
Investment Holdings [Line Items]
Other investments	46,083	40,350
Operating Entities [Member] | Real Estate Investments [Member]
Investment Holdings [Line Items]
Other investments	2,079	2,353
Operating Entities [Member] | Equity Method Investments [Member]
Investment Holdings [Line Items]
Other investments	19,443	16,687
Operating Entities [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Other investments	731	553
Consolidated Funds [Member]
Investment Holdings [Line Items]
Other investments	227,918	228,820
Consolidated Funds [Member] | Portfolio Funds [Member]
Investment Holdings [Line Items]
Other investments	221,380	221,480
Consolidated Funds [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Other investments	$ 6,538	$ 7,340