Regulatory Requirements (Details)	12 Months Ended
	Dec. 31, 2021 USD ($)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	$ 250,000
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	$ 1,500,000
Minimum net capital required, percent	2.00%
Net capital	$ 367,203,000
Net capital requirement under alternative method	6,874,000
Excess capital	360,329,000
ATM Execution LLC
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital	6,778,000
Net capital requirement under alternative method	250,000
Excess capital	6,528,000
Westminster Research
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital	18,997,000
Net capital requirement under alternative method	250,000
Excess capital	18,747,000
Cowen Financial Products LLC
Regulatory Requirements for Broker-Dealers [Line Items]
Excess capital	17,800,000
Financial resources	37,756,000
Financial resources requirement	20,000,000
Excess financial resources	17,756,000
Cowen and Company (Asia) Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	2,081,000
Financial resources requirement	385,000
Excess financial resources	1,696,000
RCG Insurance Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	300,000
Net capital	6,000,000
Options Clearing Corporation | Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	$ 2,000,000
Minimum net capital required, percent	2.00%
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	$ 52,610,000
Financial resources requirement	22,312,000
Excess financial resources	30,298,000
U.K. Financial Services Authority | Cowen Execution Services Ltd
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	16,482,000
Financial resources requirement	4,168,000
Excess financial resources	12,314,000
Minimum | Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Required net capital under commodity exchange act	45,000
Special Reserve Accounts | Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Cash and securities segregated under securities exchange commission regulation	51,800,000
PAB Reserve Bank Accounts | Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Cash and securities segregated under securities exchange commission regulation	$ 57,200,000