Regulatory Requirements	3 Months Ended
Mar. 31, 2013
Brokers and Dealers [Abstract]
Regulatory Requirements	Regulatory Requirements As registered broker‑dealers, Cowen and Company, Cowen Capital, ATM USA, Cowen Equity Finance and Cowen Securities 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 basic method permitted by the Rule, Cowen Capital is required to maintain minimum net capital, as defined, equivalent to the greater of $1.0 million or 6.667% of aggregate indebtedness. ATM USA is required to maintain minimum net capital, as defined, equivalent to the greater of $5,000 or 6.667% of aggregate indebtedness. Cowen Equity Finance is required to maintain minimum net capital, as defined, equal to $250,000. Cowen Securities is required to maintain minimum net capital, as defined, equivalent to the greater of $236,000 or 6.667% of aggregate indebtedness. The broker-dealers are not permitted to withdraw equity if certain minimum net capital requirements are not met. As of March 31, 2013, Cowen and Company had total net capital of approximately $32.7 million, which was approximately $31.7 million in excess of its minimum net capital requirement of $1.0 million. As of March 31, 2013, Cowen Capital had total net capital of approximately $3.5 million, which was approximately $2.5 million in excess of its minimum net capital requirement of $1.0 million. As of March 31, 2013, ATM USA had total net capital of approximately $520,000, which was approximately $510,000 in excess of its minimum net capital requirement of $10,000. As of March 31, 2013, Cowen Equity Finance had total net capital of approximately $8.9 million which was approximately $8.7 million in excess of its minimum net capital requirement of $250,000. As of March 31, 2013, Cowen Securities had total net capital of approximately $1.9 million which was approximately $1.7 million in excess of its minimum net capital requirement of $0.2 million. Cowen and Company, Cowen Capital and Cowen Securities are exempt from the provisions of Rule 15c3-3 under the Securities Exchange Act of 1934 as its 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 are exempt from the provisions of Rule 15c3-3 under (k)(2)(i). Proprietary accounts of introducing brokers (“PAIB”) held at the clearing broker are considered allowable assets for net capital purposes, pursuant to agreements between Cowen and Company, Cowen Capital and Cowen Securities and the clearing broker, which require, among other things, that the clearing broker performs computations for PAIB and segregates certain balances on behalf of Cowen and Company, Cowen Capital and Cowen Securities if applicable. Ramius UK Ltd. ("Ramius UK") and CIL are subject to the capital requirements of the Financial Services Authority (“FSA”) of the UK. Financial Resources, as defined, must exceed the requirement of the FSA. As of March 31, 2013, Ramius UK's Financial Resources of $0.5 million exceeded its minimum requirement of $0.1 million by $0.4 million. As of March 31, 2013, CIL's Financial Resources of $5.0 million exceeded its minimum requirement of $2.1 million by $2.9 million. CCAL (formerly known as Cowen Latitude Advisors Limited) 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 March 31, 2013, CCAL's Financial Resources of $0.8 million exceeded the minimum requirement of $0.4 million by $0.4 million.

Regulatory Requirements

As registered broker‑dealers, Cowen and Company, Cowen Capital, ATM USA, Cowen Equity Finance and Cowen Securities 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 basic method permitted by the Rule, Cowen Capital is required to maintain minimum net capital, as defined, equivalent to the greater of $1.0 million or 6.667% of aggregate indebtedness. ATM USA is required to maintain minimum net capital, as defined, equivalent to the greater of $5,000 or 6.667% of aggregate indebtedness. Cowen Equity Finance is required to maintain minimum net capital, as defined, equal to $250,000. Cowen Securities is required to maintain minimum net capital, as defined, equivalent to the greater of $236,000 or 6.667% of aggregate indebtedness. The broker-dealers are not permitted to withdraw equity if certain minimum net capital requirements are not met. As of March 31, 2013, Cowen and Company had total net capital of approximately $32.7 million, which was approximately $31.7 million in excess of its minimum net capital requirement of $1.0 million. As of March 31, 2013, Cowen Capital had total net capital of approximately $3.5 million, which was approximately $2.5 million in excess of its minimum net capital requirement of $1.0 million. As of March 31, 2013, ATM USA had total net capital of approximately $520,000, which was approximately $510,000 in excess of its minimum net capital requirement of $10,000. As of March 31, 2013, Cowen Equity Finance had total net capital of approximately $8.9 million which was approximately $8.7 million in excess of its minimum net capital requirement of $250,000. As of March 31, 2013, Cowen Securities had total net capital of approximately $1.9 million which was approximately $1.7 million in excess of its minimum net capital requirement of $0.2 million.

Cowen and Company, Cowen Capital and Cowen Securities are exempt from the provisions of Rule 15c3-3 under the Securities Exchange Act of 1934 as its 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 are exempt from the provisions of Rule 15c3-3 under (k)(2)(i).

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

Ramius UK Ltd. ("Ramius UK") and CIL are subject to the capital requirements of the Financial Services Authority (“FSA”) of the UK. Financial Resources, as defined, must exceed the requirement of the FSA. As of March 31, 2013, Ramius UK's Financial Resources of $0.5 million exceeded its minimum requirement of $0.1 million by $0.4 million. As of March 31, 2013, CIL's Financial Resources of $5.0 million exceeded its minimum requirement of $2.1 million by $2.9 million.

CCAL (formerly known as Cowen Latitude Advisors Limited) 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 March 31, 2013, CCAL's Financial Resources of $0.8 million exceeded the minimum requirement of $0.4 million by $0.4 million.