Regulatory Requirements	9 Months Ended
Regulatory Requirements	Sep. 30, 2012
Brokers and Dealers [Abstract]
Regulatory Requirements	Regulatory Requirements As registered broker‑dealers, Cowen and Company, Cowen Capital LLC (formerly known as LaBranche Capital, LLC) and ATM USA 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 LLC 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. The broker-dealers are not permitted to withdraw equity if certain minimum net capital requirements are not met. As of September 30, 2012, Cowen and Company had total net capital of approximately $31.1 million, which was approximately $30.1 million in excess of its minimum net capital requirement of $1.0 million. As of September 30, 2012, Cowen Capital, LLC had total net capital of approximately $3.1 million, which was approximately $2.1 million in excess of its minimum net capital requirement of $1.0 million. As of September 30, 2012, ATM USA had total net capital of approximately $0.6 million, which was approximately $0.5 million in excess of its minimum net capital requirement of $0.1 million. Cowen and Company, Cowen Capital LLC and ATM USA 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. 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 and Cowen Capital LLC 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 and Cowen Capital LLC, if applicable. Ramius UK Ltd. (“Ramius UK”) and Cowen International Limited (“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 September 30, 2012, Ramius UK's Financial Resources of $0.6 million exceeded its minimum requirement of $0.2 million by $0.4 million. As of September 30, 2012, CIL's Financial Resources of $4.5 million exceeded its minimum requirement of $2.3 million by $2.2 million. Cowen and Company (Asia) Limited (“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 September 30, 2012, CCAL's Financial Resources of $0.7 million exceeded the minimum requirement of $0.4 million by $0.3 million.

The entire disclosure for financial services, specifically for brokers and dealers, for the accounting period and at the balance sheet date. Disclosure may include amounts receivable from and payable to broker-dealers and clearing organizations, including securities failed to receive, deposits received for securities loaned, amounts payable to clearing organizations related to open transactions, floor brokerage payables and payables for commodities futures accounts liquidating to an equity balance on a broker-dealer's records. May also include disclosure on company's consolidation policy and a note indicating the amount of the broker-dealer's actual net capital and the amount of required net capital.

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