Income Taxes	6 Months Ended
Jun. 30, 2016
Income Taxes [Abstract]
Income Taxes	10. Income Taxes Income tax expense for the six months ended June 30, 2016 and 2015 differs from the U.S. federal statutory rate primarily due to the taxation treatment of income attributable to noncontrolling interests in IBG LLC. These noncontrolling interests are subject to U.S. taxation as partnerships. Accordingly, the income attributable to these noncontrolling interests is reported in the condensed consolidated statements of comprehensive income, but the related U.S. income tax expense attributable to these noncontrolling interests is not reported by the Company as it is the obligation of the individual partners. Income tax expense is also affected by the differing effective tax rates in foreign, state and local jurisdictions where certain of the Company’s subsidiaries are subject to corporate taxation. Deferred income taxes arise primarily due to the amortization of the deferred tax assets recognized in connection with the common stock offerings (see Note 4), differences in the valuation of financial assets and liabilities, and for other temporary differences arising from the deductibility of compensation and depreciation expenses in different time periods for book and income tax return purposes. As of and for the six months ended June 30, 2016 and 2015, the Company had no unrecognized tax and no valuation allowances on deferred tax assets were required. The Company is subject to taxation in the U.S. and various states and foreign jurisdictions. As of June 30, 2016, the Company is no longer subject to U.S. Federal and State income tax examinations for tax years prior to 2010, and to non-U.S. income tax examinations for tax years prior to 2006. As of June 30, 2016, accumulated earnings held by non‑U.S. subsidiaries totaled $1.0 billion (as of December 31, 2015 $1.0 billion). Of this amount, approximately $0.3 billion (as of December 31, 2015 $0.4 billion) is attributable to earnings of the Company’s foreign subsidiaries that are considered “pass‑through” entities for U.S. income tax purposes. Since the Company accounts for U.S. income taxes on these earnings on a current basis, no additional U.S. tax consequences would result from the repatriation of these earnings other than that which would be due arising from currency fluctuations between the time the earnings are reported for U.S. tax purposes and when they are remitted. With respect to certain of these subsidiaries’ accumulated earnings (approximately $0.2 billion and $0.3 billion as of June 30, 2016 and December 31, 2015, respectively), repatriation would result in additional foreign taxes in the form of dividend withholding tax imposed on the recipient of the distribution or dividend distribution tax imposed on the payor of the distribution. The Company has not provided for its proportionate share of these additional foreign taxes as it does not intend to repatriate these earnings in the foreseeable future. For the same reason, the Company has not provided deferred U.S. tax on cumulative translation adjustments associated with these earnings. The remainder of the accumulated earnings are attributable to non‑U.S. subsidiaries that are not considered “pass‑through” entities for U.S. tax purposes. The Company’s U.S. tax basis in the stock of most of these entities exceeds its book basis. Establishing a deferred tax asset pursuant to ASC Topic 740 is not permitted as this difference will not reverse in the foreseeable future. In the instances in which the Company’s book basis were to exceed its U.S. tax basis, no deferred tax liability would be established as the Company would consider the earnings of those entities to be indefinitely reinvested.

10. Income Taxes

Income tax expense for the six months ended June 30, 2016 and 2015 differs from the U.S. federal statutory rate primarily due to the taxation treatment of income attributable to noncontrolling interests in IBG LLC. These noncontrolling interests are subject to U.S. taxation as partnerships. Accordingly, the income attributable to these noncontrolling interests is reported in the condensed consolidated statements of comprehensive income, but the related U.S. income tax expense attributable to these noncontrolling interests is not reported by the Company as it is the obligation of the individual partners. Income tax expense is also affected by the differing effective tax rates in foreign, state and local jurisdictions where certain of the Company’s subsidiaries are subject to corporate taxation.

Deferred income taxes arise primarily due to the amortization of the deferred tax assets recognized in connection with the common stock offerings (see Note 4), differences in the valuation of financial assets and liabilities, and for other temporary differences arising from the deductibility of compensation and depreciation expenses in different time periods for book and income tax return purposes.

As of and for the six months ended June 30, 2016 and 2015, the Company had no unrecognized tax and no valuation allowances on deferred tax assets were required. The Company is subject to taxation in the U.S. and various states and foreign jurisdictions. As of June 30, 2016, the Company is no longer subject to U.S. Federal and State income tax examinations for tax years prior to 2010, and to non-U.S. income tax examinations for tax years prior to 2006.

As of June 30, 2016, accumulated earnings held by non‑U.S. subsidiaries totaled $1.0 billion (as of December 31, 2015 $1.0 billion). Of this amount, approximately $0.3 billion (as of December 31, 2015 $0.4 billion) is attributable to earnings of the Company’s foreign subsidiaries that are considered “pass‑through” entities for U.S. income tax purposes. Since the Company accounts for U.S. income taxes on these earnings on a current basis, no additional U.S. tax consequences would result from the repatriation of these earnings other than that which would be due arising from currency fluctuations between the time the earnings are reported for U.S. tax purposes and when they are remitted. With respect to certain of these subsidiaries’ accumulated earnings (approximately $0.2 billion and $0.3 billion as of June 30, 2016 and December 31, 2015, respectively), repatriation would result in additional foreign taxes in the form of dividend withholding tax imposed on the recipient of the distribution or dividend distribution tax imposed on the payor of the distribution. The Company has not provided for its proportionate share of these additional foreign taxes as it does not intend to repatriate these earnings in the foreseeable future. For the same reason, the Company has not provided deferred U.S. tax on cumulative translation adjustments associated with these earnings.

The remainder of the accumulated earnings are attributable to non‑U.S. subsidiaries that are not considered “pass‑through” entities for U.S. tax purposes. The Company’s U.S. tax basis in the stock of most of these entities exceeds its book basis. Establishing a deferred tax asset pursuant to ASC Topic 740 is not permitted as this difference will not reverse in the foreseeable future. In the instances in which the Company’s book basis were to exceed its U.S. tax basis, no deferred tax liability would be established as the Company would consider the earnings of those entities to be indefinitely reinvested.