Income taxes	6 Months Ended
Jun. 30, 2018
Income taxes
Income taxes	7. Income taxes Income tax expense of $16 and $141 reflects an effective tax rate of 0.6% and 1.8% for the three months ended June 30, 2018 and 2017, respectively. Income tax expense of $144 and $340 reflects an effective tax rate of 121.0% and 2.4% for the six months ended June 30, 2018 and 2017, respectively. Our effective tax rate differs from the statutory rate primarily due to our valuation allowance for the three and six months ended June 30, 2018 and 2017 as well as foreign tax expense for the three and six months ended June 30, 2018. 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 to resolve. We are subject to taxation in the United States and in various states. Our tax years 2014 and forward are subject to examination by the IRS and our tax years 2013 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. We are currently subject to examination by the IRS for our 2015 tax year. Although the ultimate outcome is unknown, we believe that any adjustments that may result from examination is not likely to have a material adverse effect on our condensed consolidated results of operations, financial position or cash flows.

7. Income taxes

Income tax expense of $16 and $141 reflects an effective tax rate of 0.6% and 1.8% for the three months ended June 30, 2018 and 2017, respectively. Income tax expense of $144 and $340 reflects an effective tax rate of 121.0% and 2.4% for the six months ended June 30, 2018 and 2017, respectively. Our effective tax rate differs from the statutory rate primarily due to our valuation allowance for the three and six months ended June 30, 2018 and 2017 as well as foreign tax expense for the three and six months ended June 30, 2018.

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 to resolve. We are subject to taxation in the United States and in various states. Our tax years 2014 and forward are subject to examination by the IRS and our tax years 2013 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. We are currently subject to examination by the IRS for our 2015 tax year. Although the ultimate outcome is unknown, we believe that any adjustments that may result from examination is not likely to have a material adverse effect on our condensed consolidated results of operations, financial position or cash flows.