Organization and Business	12 Months Ended
Dec. 31, 2011
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Business	Organization and Business Cowen Group, Inc., a Delaware corporation, was formed on June 1, 2009 in connection with the Transaction Agreement and Agreement and Plan of Merger (“Transaction Agreement”), dated as of June 3, 2009, by and among Cowen Holdings, Inc. (“Cowen Holdings,” formerly Cowen Group, Inc.), Lexington Merger Corp., Ramius LLC (“Ramius,” formerly Park Exchange LLC) and RCG Holdings LLC (“RCG,” formerly Ramius LLC). Cowen Group, Inc. is a diversified financial services firm and, together with its consolidated subsidiaries (collectively, “Cowen,” “Cowen Group” or the “Company”), provides alternative investment management, investment banking, research, market‑making and sales and trading services through its two business segments: alternative investment management and broker‑dealer. The Company's alternative investment segment includes hedge funds, replication products, mutual funds, managed futures funds, fund of funds, real estate, healthcare royalty funds, cash management services and mortgage advisory services offered primarily under the Ramius name. The broker‑dealer segment offers research, brokerage and investment banking services to companies and institutional investor clients primarily in the healthcare, technology, media and telecommunications, consumer, aerospace and defense, industrials, real estate investment trusts ("REITs") and alternative energy sectors, primarily under the Cowen name.

Organization and Business

Cowen Group, Inc., a Delaware corporation, was formed on June 1, 2009 in connection with the Transaction Agreement and Agreement and Plan of Merger (“Transaction Agreement”), dated as of June 3, 2009, by and among Cowen Holdings, Inc. (“Cowen Holdings,” formerly Cowen Group, Inc.), Lexington Merger Corp., Ramius LLC (“Ramius,” formerly Park Exchange LLC) and RCG Holdings LLC (“RCG,” formerly Ramius LLC).

Cowen Group, Inc. is a diversified financial services firm and, together with its consolidated subsidiaries (collectively, “Cowen,” “Cowen Group” or the “Company”), provides alternative investment management, investment banking, research, market‑making and sales and trading services through its two business segments: alternative investment management and broker‑dealer. The Company's alternative investment segment includes hedge funds, replication products, mutual funds, managed futures funds, fund of funds, real estate, healthcare royalty funds, cash management services and mortgage advisory services offered primarily under the Ramius name. The broker‑dealer segment offers research, brokerage and investment banking services to companies and institutional investor clients primarily in the healthcare, technology, media and telecommunications, consumer, aerospace and defense, industrials, real estate investment trusts ("REITs") and alternative energy sectors, primarily under the Cowen name.