Income Taxes	9 Months Ended
Sep. 30, 2015
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 that file tax returns are United Kingdom, Luxembourg, Gibraltar, and Hong Kong. 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 17.81% and 0.69% for the nine months ended September 30, 2015 and 2014, respectively. During the nine months ended September 30, 2015, the unusual or infrequent items whose tax impact were recorded discretely related primarily to state taxes, the impact of change in tax legislation in New York and the tax provisions of the Company’s foreign subsidiaries. For the nine months ended September 30, 2015, the effective tax rate differs from the statutory rate of 35% primarily due to state taxes, stock compensation and other nondeductible expenses. For the nine months ended September 30, 2014, the effective tax rate differs from the statutory rate of 35% primarily due to a change 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 September 30, 2015, the Company recorded no valuation allowance against its net deferred tax assets. The Company is subject to examination by the United States Internal Revenue Service, the United Kingdom Inland Revenue Service as well as state, local and foreign tax authorities in jurisdictions where the Company has significant business operations, such as New York. Currently, the Company is under audit by New York State for the 2010 to 2012 tax years. Management is not expecting a material tax liability from this audit. The Company intends to permanently reinvest the capital and accumulated earnings of its foreign subsidiaries in the respective subsidiary, but remits the current earnings of its foreign subsidiaries to the United States to the extent permissible under local regulatory rules. The undistributed earnings of the Company’s foreign subsidiaries totaled $0.8 million and $1.1 million as of September 30, 2015 and December 31, 2014, respectively, and the tax liability that would arise if these earnings were remitted to the United States would be approximately $0.1 million and $0.2 million, respectively.

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 that file tax returns are United Kingdom, Luxembourg, Gibraltar, and Hong Kong.

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 17.81% and 0.69% for the nine months ended September 30, 2015 and 2014, respectively. During the nine months ended September 30, 2015, the unusual or infrequent items whose tax impact were recorded discretely related primarily to state taxes, the impact of change in tax legislation in New York and the tax provisions of the Company’s foreign subsidiaries.

For the nine months ended September 30, 2015, the effective tax rate differs from the statutory rate of 35% primarily due to state taxes, stock compensation and other nondeductible expenses. For the nine months ended September 30, 2014, the effective tax rate differs from the statutory rate of 35% primarily due to a change 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 September 30, 2015, the Company recorded no valuation allowance against its net deferred tax assets.

The Company is subject to examination by the United States Internal Revenue Service, the United Kingdom Inland Revenue Service as well as state, local and foreign tax authorities in jurisdictions where the Company has significant business operations, such as New York. Currently, the Company is under audit by New York State for the 2010 to 2012 tax years. Management is not expecting a material tax liability from this audit.

The Company intends to permanently reinvest the capital and accumulated earnings of its foreign subsidiaries in the respective subsidiary, but remits the current earnings of its foreign subsidiaries to the United States to the extent permissible under local regulatory rules. The undistributed earnings of the Company’s foreign subsidiaries totaled $0.8 million and $1.1 million as of September 30, 2015 and December 31, 2014, respectively, and the tax liability that would arise if these earnings were remitted to the United States would be approximately $0.1 million and $0.2 million, respectively.