Investments of Operating Entities and Consolidated Funds - Operating Entities - Carried Interest (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Other investments		$ 255,027	$ 185,722
Carried interest
Investment Holdings [Line Items]
Other investments	[1]	82,892	30,360
Cowen Healthcare Investments II LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		62,112	23,759
Cowen Healthcare Investments III LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		11,520	0
Triartisan TGIF Partners LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		3,361	0
Triartisan ES Partners, LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		3,152	0
Triartisan PFC Partners, LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		1,455	0
Ramius Multi-Strategy Fund LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		734	0
Merger Fund | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		368	0
Other Private Investment | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[2]	0	4,737
RCG IO Renergys Sarl | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		190	1,251
Ramius Mutli-Strategy Fund LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		$ 0	$ 613

[1] In accordance with US GAAP, portfolio funds are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient are not classified in the fair value hierarchy. Carried interest and equity method investments presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.

[2] Other private investment represents the Company's closed end investment in a Portfolio Fund that invests in a wireless broadband communication provider in Italy.