Regulatory Requirements (Details)	Dec. 31, 2015 USD ($)
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	$ 1,000,000
Net capital	50,800,000
Excess capital	49,800,000
ATM Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	4,100,000
Excess capital	3,800,000
Concept (Cowen Prime)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	17,900,000
Excess capital	17,600,000
Conifer (Cowen Prime Trading)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	250,000
Net capital	3,600,000
Excess capital	3,300,000
Vianden
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	6,600,000
Net capital	64,000,000
Excess capital	58,200,000
Hollenfels
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	4,000,000
Net capital	77,400,000
Excess capital	73,400,000
RCG Insurance Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum net capital required	300,000.0
Net capital	22,000,000
U.K. Financial Services Authority | Raimus U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	280,000
Financial resources requirement	50,000
Excess financial resources	230,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	3,200,000
Financial resources requirement	2,100,000
Excess financial resources	$ 1,100,000