Income taxes	9 Months Ended
Sep. 30, 2016
Income taxes
Income taxes	6. Income taxes We calculate our interim income tax provision in accordance with ASC 270, Interim Reporting, and ASC 740, Accounting for Income Taxes. At the end of each interim period, we estimate the annual effective tax rate and apply that rate to our ordinary quarterly earnings. The tax expense or benefit related to significant, unusual, or extraordinary items is recognized in the interim period in which those items occur. In addition, the effect of changes in enacted tax laws, rates, or tax status is recognized in the interim period in which the change occurs. As noted above, we early adopted ASU 2016-09 as of January 1, 2016. As a result of the adoption of ASU 2016-09, excess windfall tax benefits and tax deficiencies related to our stock option exercises and RSU vestings are recognized as an income tax benefit or expense in our condensed consolidated statements of operations in the period they are deducted on the income tax return. Excess windfall tax benefits and tax deficiencies are therefore not anticipated when determining the annual effective tax rate and are instead recognized in the interim period in which those items occur. The computation of the annual estimated effective tax rate at each interim period requires certain estimates and significant judgment, including the expected operating income (loss) for the year, projections of the proportion of income (loss) earned and taxed in various states, permanent and temporary differences as a result of differences between amounts measured and recognized in accordance with tax laws and financial accounting standards, and the likelihood of recovering deferred tax assets generated in the current year. The accounting estimates used to compute the provision for income taxes may change as new events occur, additional information is obtained, or as the tax environment changes. Income tax expense of $95 and $115 reflects an effective tax rate of 1.8% and 2.4% for the three months ended September 30, 2016 and 2015, respectively. Income tax expense of $457 and $401 reflects an effective tax rate of 2.1% and 2.2% for the nine months ended September 30, 2016 and 2015, respectively. Our effective tax rate differs from the statutory rate primarily due to our valuation allowance for the three and nine months ended September 30, 2016 and 2015. The adoption of ASU 2016-09 did not have any impact on our income tax expense for the three and nine months ended September 30, 2016 due to our valuation allowance. As of September 30, 2016 and December 31, 2015, we had $376 and $363 of uncertain tax positions, respectively, $84 of which is a reduction to deferred tax assets, which is presented net of uncertain tax positions, in the accompanying condensed consolidated balance sheets. We accrue interest and penalties related to unrecognized tax benefits as a component of income taxes. As of September 30, 2016 and December 31, 2015, we have accrued $63 and $50 for related interest, net of federal income tax benefits, and penalties recorded in income tax expense on our condensed consolidated statements of operations, respectively. The amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate at September 30, 2016 was $229. We operate within federal, state and international taxing jurisdictions and are subject to audit in these jurisdictions. These audits can involve complex issues which may require an extended period of time to resolve. We are subject to taxation in the United States and in various states. Our tax years 2013 and forward are subject to examination by the IRS and our tax years 2011 and forward are subject to examination by material state jurisdictions. However, due to prior year loss carryovers, the IRS and state tax authorities may examine any tax years for which the carryovers are used to offset future taxable income.

6. Income taxes

We calculate our interim income tax provision in accordance with ASC 270, Interim Reporting, and ASC 740, Accounting for Income Taxes. At the end of each interim period, we estimate the annual effective tax rate and apply that rate to our ordinary quarterly earnings. The tax expense or benefit related to significant, unusual, or extraordinary items is recognized in the interim period in which those items occur. In addition, the effect of changes in enacted tax laws, rates, or tax status is recognized in the interim period in which the change occurs. As noted above, we early adopted ASU 2016-09 as of January 1, 2016. As a result of the adoption of ASU 2016-09, excess windfall tax benefits and tax deficiencies related to our stock option exercises and RSU vestings are recognized as an income tax benefit or expense in our condensed consolidated statements of operations in the period they are deducted on the income tax return. Excess windfall tax benefits and tax deficiencies are therefore not anticipated when determining the annual effective tax rate and are instead recognized in the interim period in which those items occur.

The computation of the annual estimated effective tax rate at each interim period requires certain estimates and significant judgment, including the expected operating income (loss) for the year, projections of the proportion of income (loss) earned and taxed in various states, permanent and temporary differences as a result of differences between amounts measured and recognized in accordance with tax laws and financial accounting standards, and the likelihood of recovering deferred tax assets generated in the current year. The accounting estimates used to compute the provision for income taxes may change as new events occur, additional information is obtained, or as the tax environment changes.

Income tax expense of $95 and $115 reflects an effective tax rate of 1.8% and 2.4% for the three months ended September 30, 2016 and 2015, respectively. Income tax expense of $457 and $401 reflects an effective tax rate of 2.1% and 2.2% for the nine months ended September 30, 2016 and 2015, respectively. Our effective tax rate differs from the statutory rate primarily due to our valuation allowance for the three and nine months ended September 30, 2016 and 2015. The adoption of ASU 2016-09 did not have any impact on our income tax expense for the three and nine months ended September 30, 2016 due to our valuation allowance. As of September 30, 2016 and December 31, 2015, we had $376 and $363 of uncertain tax positions, respectively, $84 of which is a reduction to deferred tax assets, which is presented net of uncertain tax positions, in the accompanying condensed consolidated balance sheets. We accrue interest and penalties related to unrecognized tax benefits as a component of income taxes. As of September 30, 2016 and December 31, 2015, we have accrued $63 and $50 for related interest, net of federal income tax benefits, and penalties recorded in income tax expense on our condensed consolidated statements of operations, respectively. The amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate at September 30, 2016 was $229.

We operate within federal, state and international taxing jurisdictions and are subject to audit in these jurisdictions. These audits can involve complex issues which may require an extended period of time to resolve. We are subject to taxation in the United States and in various states. Our tax years 2013 and forward are subject to examination by the IRS and our tax years 2011 and forward are subject to examination by material state jurisdictions. However, due to prior year loss carryovers, the IRS and state tax authorities may examine any tax years for which the carryovers are used to offset future taxable income.