Regulatory Requirements	12 Months Ended
Dec. 31, 2014
Brokers and Dealers [Abstract]
Regulatory Requirements	Regulatory Requirements As registered broker-dealers, Cowen and Company, ATM Execution, ATM USA, and Cowen Equity Finance 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, ATM USA and Cowen Equity Finance are each 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 December 31, 2014, Cowen and Company had total net capital of approximately $42.9 million, which was approximately$41.9 million in excess of its minimum net capital requirement of $1.0 million. As of December 31, 2014, ATM Execution had total net capital of approximately $3.1 million, which was approximately $2.8 million in excess of its minimum net capital requirement of $250,000. As of December 31, 2014, ATM USA had total net capital of approximately $1.1 million, which was approximately $0.8 million in excess of its minimum net capital requirement of $250,000. As of December 31, 2014, Cowen Equity Finance had total net capital of approximately $14.9 million which was approximately $14.6 million in excess of its minimum net capital requirement of $250,000. In January 2015, ATM USA and Cowen Equity Finance each filed form BDW Uniform Requests for Withdrawal from Broker-Dealer Registration with FINRA which have not yet been approved. Accordingly both broker dealers were still subject to the SEC's Uniform Net Capital Rule 15c3-1 as of December 31, 2014. Cowen and Company and ATM Execution 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. Similarly, ATM USA and Cowen Equity Finance claim exemption from the provisions of Rule 15c3-3 under (k)(2)(i). 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 and ATM Execution, 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 December 31, 2014, Ramius UK's Financial Resources of $0.32 million exceeded its minimum requirement of $0.11 million by $0.21 million. As of December 31, 2014, CIL's Financial Resources of $3.3 million exceeded its minimum requirement of $2.2 million by $1.1 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 December 31, 2014, 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, ATM USA, and Cowen Equity Finance 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, ATM USA and Cowen Equity Finance are each 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 December 31, 2014, Cowen and Company had total net capital of approximately $42.9 million, which was approximately$41.9 million in excess of its minimum net capital requirement of $1.0 million. As of December 31, 2014, ATM Execution had total net capital of approximately $3.1 million, which was approximately $2.8 million in excess of its minimum net capital requirement of $250,000. As of December 31, 2014, ATM USA had total net capital of approximately $1.1 million, which was approximately $0.8 million in excess of its minimum net capital requirement of $250,000. As of December 31, 2014, Cowen Equity Finance had total net capital of approximately $14.9 million which was approximately $14.6 million in excess of its minimum net capital requirement of $250,000. In January 2015, ATM USA and Cowen Equity Finance each filed form BDW Uniform Requests for Withdrawal from Broker-Dealer Registration with FINRA which have not yet been approved. Accordingly both broker dealers were still subject to the SEC's Uniform Net Capital Rule 15c3-1 as of December 31, 2014.

Cowen and Company and ATM Execution 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. Similarly, ATM USA and Cowen Equity Finance claim exemption from the provisions of Rule 15c3-3 under (k)(2)(i).

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 and ATM Execution, 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 December 31, 2014, Ramius UK's Financial Resources of $0.32 million exceeded its minimum requirement of $0.11 million by $0.21 million. As of December 31, 2014, CIL's Financial Resources of $3.3 million exceeded its minimum requirement of $2.2 million by $1.1 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 December 31, 2014, Cowen Asia's Financial Resources of $0.5 million exceeded the minimum requirement of $0.4 million by $0.1 million.