Regulatory Requirements (Details) (USD $)	Jun. 30, 2014
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	$ 1,000,000
Net capital	70,800,000
Excess capital	69,800,000
ATM Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	3,800,000
Excess capital	3,600,000
ATM USA
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	900,000
Excess capital	700,000
Cowen Equity Finance
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	14,200,000
Excess capital	13,900,000
U.K. Financial Services Authority | Raimus U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	360,000
Financial resources requirement	120,000
Excess financial resources	240,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	3,600,000
Financial resources requirement	2,200,000
Excess financial resources	1,400,000
H.K. Securities and Futures Commission | Cowen and Company (Asia) Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	800,000
Financial resources requirement	400,000
Excess financial resources	$ 400,000