Regulatory Requirements (Details) (USD $)	Dec. 31, 2013
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	$ 1,000,000
Net capital	36,400,000
Excess capital	35,400,000
ATM Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	2,700,000
Excess capital	2,400,000
ATM USA
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	1,200,000
Excess capital	900,000
Cowen Equity Finance
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	12,000,000
Excess capital	11,700,000
U.K. Financial Services Authority | Raimus U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	350,000
Financial resources requirement	180,000
Excess financial resources	170,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	4,400,000
Financial resources requirement	2,200,000
Excess financial resources	2,200,000
H.K. Securities and Futures Commission | Cowen and Company (Asia) Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	1,100,000
Financial resources requirement	400,000
Excess financial resources	$ 700,000