Regulatory Requirements	9 Months Ended
Sep. 30, 2015
Brokers and Dealers [Abstract]
Regulatory Requirements	Regulatory Requirements As registered broker-dealers, Cowen and Company, ATM Execution and Cowen Prime are subject to the SEC's Uniform Net Capital Rule 15c3-1 (the “Rule”), which requires the maintenance of minimum net capital. Under the alternative method permitted by the Rule, Cowen and Company's minimum net capital requirement, as defined, is $1.0 million. Under the alternative method ATM Execution and Cowen Prime are required to maintain minimum net capital, as defined, equal to $250,000. The broker-dealers are not permitted to withdraw equity if certain minimum net capital requirements are not met. As of September 30, 2015, Cowen and Company had total net capital of approximately $123.4 million, which was approximately $122.4 million in excess of its minimum net capital requirement of $1.0 million. As of September 30, 2015, ATM Execution had total net capital of approximately $4.7 million, which was approximately $4.4 million in excess of its minimum net capital requirement of $250,000. As of September 30, 2015, Cowen Prime had total net capital of approximately $4.2 million, which was approximately $3.9 million in excess of its minimum net capital requirement of $250,000. Cowen and Company, ATM Execution and Cowen Prime claim exemption from the provisions of Rule 15c3-3 under the Securities Exchange Act of 1934 as their activities are limited to those set forth in the conditions for exemption appearing in paragraph (k)(2)(ii) of the Rule. Proprietary accounts of broker dealers (“PAB”) held at the clearing broker are considered allowable assets for net capital purposes, pursuant to agreements between Cowen and Company and ATM Execution and the clearing broker, which require, among other things, that the clearing broker performs computations for PAB and segregates certain balances on behalf of Cowen and Company, ATM Execution and Cowen Prime, if applicable. Ramius UK Ltd. ("Ramius UK") and Cowen International Limited ("CIL") are subject to the capital requirements of the Financial Conduct Authority (“FCA”) of the UK. Financial Resources, as defined, must exceed the requirement of the FCA. As of September 30, 2015, Ramius UK's Financial Resources of $0.29 million exceeded its minimum requirement of $0.06 million by $0.2 million. As of September 30, 2015, CIL's Financial Resources of $3.3 million exceeded its minimum requirement of $2.0 million by $1.3 million. Cowen and Company (Asia) Limited (“Cowen Asia”) is subject to the financial resources requirements of the Securities and Futures Commission (“SFC”) of Hong Kong. Financial Resources, as defined, must exceed the Total Financial Resources requirement of the SFC. As of September 30, 2015, Cowen Asia's Financial Resources of $0.5 million exceeded the minimum requirement of $0.4 million by $0.1 million.

Regulatory Requirements

As registered broker-dealers, Cowen and Company, ATM Execution and Cowen Prime are subject to the SEC's Uniform Net Capital Rule 15c3-1 (the “Rule”), which requires the maintenance of minimum net capital. Under the alternative method permitted by the Rule, Cowen and Company's minimum net capital requirement, as defined, is $1.0 million. Under the alternative method ATM Execution and Cowen Prime are required to maintain minimum net capital, as defined, equal to $250,000. The broker-dealers are not permitted to withdraw equity if certain minimum net capital requirements are not met. As of September 30, 2015, Cowen and Company had total net capital of approximately $123.4 million, which was approximately $122.4 million in excess of its minimum net capital requirement of $1.0 million. As of September 30, 2015, ATM Execution had total net capital of approximately $4.7 million, which was approximately $4.4 million in excess of its minimum net capital requirement of $250,000. As of September 30, 2015, Cowen Prime had total net capital of approximately $4.2 million, which was approximately $3.9 million in excess of its minimum net capital requirement of $250,000.

Cowen and Company, ATM Execution and Cowen Prime claim exemption from the provisions of Rule 15c3-3 under the Securities Exchange Act of 1934 as their activities are limited to those set forth in the conditions for exemption appearing in paragraph (k)(2)(ii) of the Rule.

Proprietary accounts of broker dealers (“PAB”) held at the clearing broker are considered allowable assets for net capital purposes, pursuant to agreements between Cowen and Company and ATM Execution and the clearing broker, which require, among other things, that the clearing broker performs computations for PAB and segregates certain balances on behalf of Cowen and Company, ATM Execution and Cowen Prime, if applicable.

Ramius UK Ltd. ("Ramius UK") and Cowen International Limited ("CIL") are subject to the capital requirements of the Financial Conduct Authority (“FCA”) of the UK. Financial Resources, as defined, must exceed the requirement of the FCA. As of September 30, 2015, Ramius UK's Financial Resources of $0.29 million exceeded its minimum requirement of $0.06 million by $0.2 million. As of September 30, 2015, CIL's Financial Resources of $3.3 million exceeded its minimum requirement of $2.0 million by $1.3 million.

Cowen and Company (Asia) Limited (“Cowen Asia”) is subject to the financial resources requirements of the Securities and Futures Commission (“SFC”) of Hong Kong. Financial Resources, as defined, must exceed the Total Financial Resources requirement of the SFC. As of September 30, 2015, Cowen Asia's Financial Resources of $0.5 million exceeded the minimum requirement of $0.4 million by $0.1 million.