Investments of Operating Entities and Consolidated Funds - Other Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018		Dec. 31, 2017
Investment Holdings [Line Items]
Other investments	$ 167,428		$ 141,548
Portfolio Funds, Consolidated Funds	183,290		374,111
Portfolio Funds, at fair value
Investment Holdings [Line Items]
Other investments	125,107	[1]	100,148	[2]
Equity Method Investments
Investment Holdings [Line Items]
Other investments	42,321		41,099
Lehman claims, at fair value
Investment Holdings [Line Items]
Other investments	0		301
Enterprise LP [Member]
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	97,026		87,221
Merger Fund [Member]
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	$ 86,264		$ 286,890

[1] In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated statement of financial condition.

[2] In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated statement of financial condition.