Regulatory Requirements (Details)	Mar. 31, 2016 USD ($)
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	$ 1,000,000
Net capital	56,600,000
Excess capital	55,600,000
Concept (Cowen Prime)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	17,500,000
Excess capital	17,300,000
Conifer (Cowen Prime Trading)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	4,400,000
Excess capital	4,200,000
RCG Insurance Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	300,000.0
Net capital	21,000,000
ATM Execution LLC [Member]
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	3,900,000
Excess capital	3,700,000
U.K. Financial Services Authority | Raimus U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	280,000
Financial resources requirement	60,000
Excess financial resources	220,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	4,300,000
Financial resources requirement	2,000,000
Excess financial resources	$ 2,300,000