7. 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.

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 $115 and $75 reflects an effective tax rate of 2.4% and 2.2% for the three months ended September 30, 2015 and 2014, respectively. Income tax expense of $401 and $378 reflects an effective tax rate of 2.2% and 3.1% for the nine months ended September 30, 2015 and 2014, 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, 2015 and 2014. At September 30, 2015, we have net deferred tax liabilities of $2,930. As of September 30, 2015 and December 31, 2014, we had $359 and $459, respectively, of uncertain tax positions, $84 and $106, respectively, 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, 2015 and December 31, 2014, we have accrued $46 and $67, respectively, for related interest, net of federal income tax benefits, and penalties. The amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate as of September 30, 2015 was $229.

A reconciliation of our unrecognized tax benefits, excluding interest and penalties, is as follows:

Beginning balance, January 1, 2015	$	392
Additions for current period tax positions	—
Effective settlement during the current period	(79		)

Balance, September 30, 2015	$	313

We are subject to taxation in the United States and in various states. Our tax years 2012 and forward are subject to examination by the IRS and our tax years 2010 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.