Regulatory Requirements	12 Months Ended
Dec. 31, 2016
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 December 31, 2016, Cowen and Company had total net capital of approximately $65.3 million, which was approximately $64.3 million in excess of its minimum net capital requirement of $1.0 million. As of December 31, 2016, ATM Execution had total net capital of approximately $3.5 million, which was approximately $3.2 million in excess of its minimum net capital requirement of $250,000. As of December 31, 2016, Cowen Prime had total net capital of approximately $13.9 million, which was approximately $13.6 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, ATM Execution and Cowen Prime and the clearing brokers, which require, among other things, that the clearing brokers perform computations for PAB and segregate 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 December 31, 2016, Ramius UK's Financial Resources of $0.22 million exceeded its minimum requirement of $0.05 million by $0.17 million. As of December 31, 2016, CIL's Financial Resources of $9.6 million exceeded its minimum requirement of $2.6 million by $7.0 million. Cowen’s Luxembourg reinsurance companies, Vianden RCG Re SCA (“Vianden”) and Hollenfels, are required to maintain a solvency capital ratio as calculated by relevant European Commission directives and local regulatory rules in Luxembourg. Each company’s solvency capital ratio as of December 31, 2016 was in excess of this minimum requirement. Based on minimum capital and surplus requirements pursuant to the laws of the state of New York that apply to captive insurance companies, RCG Insurance Company, Cowen’s captive insurance company incorporated and licensed in the state of New York, was required to maintain capital and surplus of approximately $0.3 million as of December 31, 2016. RCG Insurance Company’s capital and surplus as of December 31, 2016 totaled approximately $22.5 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 December 31, 2016, Cowen and Company had total net capital of approximately $65.3 million, which was approximately $64.3 million in excess of its minimum net capital requirement of $1.0 million. As of December 31, 2016, ATM Execution had total net capital of approximately $3.5 million, which was approximately $3.2 million in excess of its minimum net capital requirement of $250,000. As of December 31, 2016, Cowen Prime had total net capital of approximately $13.9 million, which was approximately $13.6 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, ATM Execution and Cowen Prime and the clearing brokers, which require, among other things, that the clearing brokers perform computations for PAB and segregate 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 December 31, 2016, Ramius UK's Financial Resources of $0.22 million exceeded its minimum requirement of $0.05 million by $0.17 million. As of December 31, 2016, CIL's Financial Resources of $9.6 million exceeded its minimum requirement of $2.6 million by $7.0 million.

Cowen’s Luxembourg reinsurance companies, Vianden RCG Re SCA (“Vianden”) and Hollenfels, are required to maintain a solvency capital ratio as calculated by relevant European Commission directives and local regulatory rules in Luxembourg. Each company’s solvency capital ratio as of December 31, 2016 was in excess of this minimum requirement.

Based on minimum capital and surplus requirements pursuant to the laws of the state of New York that apply to captive insurance companies, RCG Insurance Company, Cowen’s captive insurance company incorporated and licensed in the state of New York, was required to maintain capital and surplus of approximately $0.3 million as of December 31, 2016. RCG Insurance Company’s capital and surplus as of December 31, 2016 totaled approximately $22.5 million.