We made provisions for income taxes in the years ended December 31, 2017 and 2016 of $1.0 million and $2.1 million, respectively. We recorded a benefit from income taxes of $0.5 million in the year ended December 31, 2015. The components of the provision for income taxes are as follows (in thousands):

A reconciliation of the U.S. federal statutory rate to the effective tax rate is as follows:

Total income tax expense for the year ended December 31, 2017 was $1.0 million. Income tax expense for 2017 was based on: i) the U.S. statutory rate of 34%, ii) increased by the impact of the federal rate change on deferred tax assets due to enactment of the Tax Cuts and Jobs Act, iii) increased by state income taxes; and iv) reduced by permanent adjustments and research tax credits.

On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act. This legislation makes significant change in U.S. tax law including a reduction in the corporate tax rates, changes to net operating loss carryforwards and carrybacks, and a repeal of the corporate alternative minimum tax. The legislation reduced the U.S. corporate tax rate from the current rate of 34% to 21%. As a result of the enacted law, the Company was required to revalue deferred tax assets and liabilities at the enacted rate. This revaluation resulted in a provision of $0.4 million to income tax expense in continuing operations and a corresponding reduction in the deferred tax assets.

Total income tax expense for the year ended December 31, 2016 was $2.1 million. Income tax expense in 2016 was based on the U.S. statutory rate of 34%, increased by state income taxes, and reduced by permanent adjustments and research tax credits.

We recorded a benefit from income taxes of $0.5 million for the year ended December 31, 2015. The benefit from income taxes was the result of a $1.9 million tax benefit from the reversal of a reserve for uncertain tax positions, which was partially offset by $1.4 million of income taxes on pre-tax income based on the U.S. statutory rate of 34%, increased by state income taxes, and reduced by research tax credits and permanent adjustments.

As previously reported, the Internal Revenue Service (“IRS”) commenced an examination of our tax return for the year ended December 31, 2012 in September 2014. In July 2015, the IRS notified us that it had completed its examination and that it had no changes to our reported tax. As a result of the completion of the IRS examination, we determined that the $1.9 million reserve for uncertain tax positions we had established on federal research and development credits in 2012 was no longer required. We reversed the reserve in 2015.

As of December 31, 2017 and 2016, we had deferred tax assets for which we had recorded no valuation allowance. The principal components of deferred tax assets were as follows at December 31 (in thousands):

As of December 31, 2017, we had a total of $5.4 million of deferred tax assets for which we had recorded no valuation allowance. We have assessed the need for a valuation allowance on our deferred tax assets.  Based on our assessment of future sources of income, including reversing deferred tax liabilities, and future earnings, we have determined that it is more likely than not that the deferred tax assets will be realized, and therefore there is no valuation allowance required for the deferred tax assets. We will continue to assess the level of valuation allowance in future periods. Should evidence regarding the realizability of tax assets change at a future point in time, the valuation allowance will be adjusted accordingly.

A rollforward of the uncertain tax position related to our research and development tax credits is as follows (in thousands):

Uncertain tax positions of $0.7 million will impact our tax rate if realized. The difference between this amount and the total uncertain tax positions in the table above is the federal tax effect on state tax credits.

At December 31, 2016, in addition to deferred tax assets carried on our balance sheet, we also had net federal research and development credit carryforwards available of $4.8 million. Under the income tax rules at that time, these credits were not recorded as tax assets as they relate to excess stock compensation deductions and could not be recorded as tax assets until the amounts had been utilized to reduce our tax liability. To the extent that these assets were used to reduce taxes in 2016, and 2015, the benefits were recorded as a reduction to additional paid-in capital. In 2016 and 2015, we recorded tax benefits to additional paid-in capital of $0.7 million, and $0.6 million, respectively. We adopted ASU 2016-09 in 2017 which was applied using a modified retrospective approach. Upon adoption, we recorded a deferred tax asset of $4.8 million with an offsetting adjustment to retained earnings related to excess stock compensation deductions that were not previously recorded as tax assets. We utilized $0.2 million of these tax assets in 2017.

Our policy is to recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2017, we had no accrued interest or penalties related to uncertain tax positions.

The tax years from 2014 through 2017 are subject to examination by the IRS and the tax years 2001 through 2017 are subject to examination by state tax authorities. In the second quarter of 2017, the Internal Revenue Service commenced an examination of our tax return for the year ended December 31, 2015. The examination has just started and we do not have any indication of the outcome of this examination at this time.