Investments of Operating Entities and Consolidated Funds - Lehman Claims (Details) (USD $)	1 Months Ended
	Feb. 29, 2012	Dec. 31, 2011	Jul. 31, 2010	Jun. 30, 2010	Sep. 30, 2012	Sep. 15, 2008
Investment Holdings [Line Items]
Other investments		$ 59,943,000			$ 70,151,000
Operating Entities [Member]
Investment Holdings [Line Items]
Other investments		59,943,000			70,151,000
Operating Entities [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Initial value					1,000,000
Claim settlement receivable					900,000
Estimated recoverable percent		47.00%			27.00%
Other investments		553,000			761,000
Consolidated Funds [Member]
Investment Holdings [Line Items]
Other investments		228,820,000			205,095,000
Consolidated Funds [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Other investments		7,340,000			6,860,000
Enterprise Master [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Initial value					12,400,000	24,300,000
Claim settlement receivable					1,100,000
Assets returned		2,400,000		9,500,000
Proceeds from sale of returned assets			10,700,000
Distributions of proceeds from returned assets	2,900,000			10,700,000
Other investments					8,600,000
Recoverable claims assigned to variable interest entities					100.00%
Enterprise Master [Member] | Trust Assets [Member]
Investment Holdings [Line Items]
Claim Resolution Agreement fee					1.00%
Enterprise Master [Member] | U.S. Denominated Assets [Member]
Investment Holdings [Line Items]
Estimated recoverable percent					73.00%
Enterprise Master [Member] | Foreign Denominated Assets [Member]
Investment Holdings [Line Items]
Estimated recoverable percent					73.00%
Enterprise Master [Member] | Unsecured Claim [Member]
Investment Holdings [Line Items]
Estimated recoverable percent					73.00%
Enterprise Master [Member] | Cash [Member]
Investment Holdings [Line Items]
Initial value					5,300,000
Estimated recoverable percent					69.00%
Other investments					3,600,000
Enterprise LP [Member] | Lehman Claim [Member]
Investment Holdings [Line Items]
Other investments					$ 6,900,000