Income Taxes	3 Months Ended
Mar. 31, 2013
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The taxable results of the Company's U.S. operations are included in the consolidated income tax returns of Cowen Group, Inc. as well as stand‑alone state and local tax returns. The Company has subsidiaries that are resident in foreign countries where tax filings have to be submitted on a stand‑alone basis. These subsidiaries are subject to tax in their respective countries and the Company is responsible for and, thus, reports all taxes incurred by these subsidiaries. The countries where the Company owns subsidiaries are United Kingdom, Germany, Luxembourg, Gibraltar, Japan, Hong Kong, and China. The Company calculates its U.S. tax provision using the estimated annual effective tax rate methodology. The tax expense or benefit caused by an unusual or infrequent item is recorded in the quarter in which it occurs. The Company uses the discrete methodology to calculate its income tax provision for its foreign subsidiaries. Based on these methodologies, the Company's effective income tax rate was 16.07% and 2.22% for the three months ended March 31, 2013 and 2012, respectively. During the three months ended March 31, 2013, the unusual or infrequent item whose tax impact was recorded discretely was primarily related to the tax provisions of the Company's foreign subsidiaries. For the three months ended March 31, 2013 and 2012, the effective tax rate differs from the statutory rate of 35% primarily due to an increase in the Company's valuation allowance, stock compensation and other nondeductible expenses. The Company records deferred tax assets and liabilities for the future tax benefit or expense that will result from differences between the carrying value of its assets for income tax purposes and for financial reporting purposes, as well as for operating or capital loss and tax credit carryovers. A valuation allowance is recorded to bring the net deferred tax assets to a level that, in management's view, is more likely than not to be realized in the foreseeable future. This level will be estimated based on a number of factors, especially the amount of net deferred tax assets of the Company that are actually expected to be realized, for tax purposes, in the foreseeable future. As of March 31, 2013 the Company recorded a valuation allowance against substantially all of its net deferred tax assets. The Company is subject to examination by the United States Internal Revenue Service (IRS), the United Kingdom Inland Revenue Service and state and local and foreign tax authorities in jurisdictions where the Company has significant business operations, such as New York. Currently, one of the Company's former consolidated tax groups is under examination by the IRS for its 2010 tax year. No significant adjustments are expected as a result of this audit. The Company intends to permanently reinvest the capital and accumulated earnings of its foreign subsidiaries in the respective subsidiary, but repatriates the current earnings of its foreign subsidiaries to the United States to the extent such repatriation is permissible under local regulatory rules. The undistributed earnings of the Company's foreign subsidiaries totaled $2.3 million as of March 31, 2013. The tax liability that would arise if these earnings were remitted to the United States is approximately $0.3 million.

Income Taxes

3 Months Ended

Mar. 31, 2013

The taxable results of the Company's U.S. operations are included in the consolidated income tax returns of Cowen Group, Inc. as well as stand‑alone state and local tax returns. The Company has subsidiaries that are resident in foreign countries where tax filings have to be submitted on a stand‑alone basis. These subsidiaries are subject to tax in their respective countries and the Company is responsible for and, thus, reports all taxes incurred by these subsidiaries. The countries where the Company owns subsidiaries are United Kingdom, Germany, Luxembourg, Gibraltar, Japan, Hong Kong, and China.

The Company calculates its U.S. tax provision using the estimated annual effective tax rate methodology. The tax expense or benefit caused by an unusual or infrequent item is recorded in the quarter in which it occurs. The Company uses the discrete methodology to calculate its income tax provision for its foreign subsidiaries. Based on these methodologies, the Company's effective income tax rate was 16.07% and 2.22% for the three months ended March 31, 2013 and 2012, respectively. During the three months ended March 31, 2013, the unusual or infrequent item whose tax impact was recorded discretely was primarily related to the tax provisions of the Company's foreign subsidiaries.

For the three months ended March 31, 2013 and 2012, the effective tax rate differs from the statutory rate of 35% primarily due to an increase in the Company's valuation allowance, stock compensation and other nondeductible expenses.

The Company records deferred tax assets and liabilities for the future tax benefit or expense that will result from differences between the carrying value of its assets for income tax purposes and for financial reporting purposes, as well as for operating or capital loss and tax credit carryovers. A valuation allowance is recorded to bring the net deferred tax assets to a level that, in management's view, is more likely than not to be realized in the foreseeable future. This level will be estimated based on a number of factors, especially the amount of net deferred tax assets of the Company that are actually expected to be realized, for tax purposes, in the foreseeable future. As of March 31, 2013 the Company recorded a valuation allowance against substantially all of its net deferred tax assets.

The Company is subject to examination by the United States Internal Revenue Service (IRS), the United Kingdom Inland Revenue Service and state and local and foreign tax authorities in jurisdictions where the Company has significant business operations, such as New York. Currently, one of the Company's former consolidated tax groups is under examination by the IRS for its 2010 tax year. No significant adjustments are expected as a result of this audit.

The Company intends to permanently reinvest the capital and accumulated earnings of its foreign subsidiaries in the respective subsidiary, but repatriates the current earnings of its foreign subsidiaries to the United States to the extent such repatriation is permissible under local regulatory rules. The undistributed earnings of the Company's foreign subsidiaries totaled $2.3 million as of March 31, 2013. The tax liability that would arise if these earnings were remitted to the United States is approximately $0.3 million.