Investments in Partnerships, Offshore Funds and Variable Interest Entities, Summary of partnership investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Fair Value	$ 26,128	$ 27,122
Equity Method	71,421	73,771
Total	97,549	100,893
Consolidated Feeder Funds [Member] | Affiliated Entity [Member]
Schedule of Equity Method Investments [Line Items]
Fair Value	26,128	27,122
Equity Method	0	0
Total	26,128	27,122
Partnership [Member] | Affiliated Entity [Member]
Schedule of Equity Method Investments [Line Items]
Fair Value	0	0
Equity Method	28,158	34,135
Total	28,158	34,135
Partnership [Member] | Unaffiliated [Member]
Schedule of Equity Method Investments [Line Items]
Fair Value	0	0
Equity Method	6,505	7,610
Total	6,505	7,610
Offshore Funds [Member] | Affiliated Entity [Member]
Schedule of Equity Method Investments [Line Items]
Fair Value	0	0
Equity Method	29,679	25,588
Total	29,679	25,588
Offshore Funds [Member] | Unaffiliated [Member]
Schedule of Equity Method Investments [Line Items]
Fair Value	0	0
Equity Method	7,079	6,438
Total	$ 7,079	$ 6,438