Regulatory Requirements (Details)	Sep. 30, 2015 USD ($)
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	$ 1,000,000
Net capital	123,400,000
Excess capital	122,400,000
ATM Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	4,700,000
Excess capital	4,400,000
Concept (Cowen Prime)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	4,200,000
Excess capital	3,900,000
U.K. Financial Services Authority | Raimus U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	290,000
Financial resources requirement	60,000
Excess financial resources	230,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	3,300,000
Financial resources requirement	2,000,000
Excess financial resources	1,300,000
H.K. Securities and Futures Commission | Cowen and Company (Asia) Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	500,000
Financial resources requirement	400,000
Excess financial resources	$ 100,000