Regulatory Requirements (Details)	Jun. 30, 2016 USD ($)
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	$ 1,000,000
Net capital	63,500,000
Excess capital	62,500,000
Concept (Cowen Prime)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	13,700,000
Excess capital	13,400,000
Conifer (Cowen Prime Trading)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
RCG Insurance Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	300,000.0
Net capital	24,600,000
ATM Execution LLC [Member]
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	3,400,000
Excess capital	3,100,000
U.K. Financial Services Authority | Ramius U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	250,000
Financial resources requirement	60,000
Excess financial resources	190,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	4,000,000
Financial resources requirement	2,000,000
Excess financial resources	$ 2,000,000