Investments of Operating Entities and Consolidated Funds - Operating Entities - Carried Interest (Details) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021
Investment Holdings [Line Items]
Other investments		$ 237,628	$ 274,111
Carried interest
Investment Holdings [Line Items]
Other investments	[1]	70,281	88,925
Cowen Healthcare Investments II LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		13,886	23,327
Cowen Healthcare Investments III LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		11,510	18,523
Cowen Sustainable Investments I LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		6,725	7,436
Cowen Sustainable Investments Offshore I LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		8,114	9,196
CSI I Prodigy Co-Investment LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		2,241	2,436
CSI PRTA Co-Investment LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		8,682	9,535
Triartisan TGIF Partners LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		4,279	4,047
Triartisan ES Partners, LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		3,389	3,401
Triartisan PFC Partners, LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		10,408	9,394
Ramius Multi-Strategy Fund LP | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		555	587
Ramius Merger Fund LLC | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		368	861
RCG IO Renergys Sarl | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		124	136
Other Funds | Carried interest | Affiliated Entity
Investment Holdings [Line Items]
Other investments		$ 0	$ 46

[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 condensed consolidated statement of financial condition.