Income Taxes	6 Months Ended
Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	(4) Income Taxes Fastenal files income tax returns in the United States federal jurisdiction, all states, and various local and foreign jurisdictions. With limited exceptions, we are no longer subject to income tax examinations by taxing authorities for taxable years before 2015 in the case of United States federal examinations, and 2013 in the case of foreign, state, and local examinations. During the first six months of 2018, there were no material changes in unrecognized tax benefits. On December 22, 2017, the Tax Act was signed into law. The Tax Act made broad and complex changes to the U.S. tax code which include: a lowering of the U.S. federal corporate income tax rate from 35% to 21% effective January 1, 2018, accelerated expensing of qualified capital investments for a specific period, and a transition from a worldwide to a territorial tax system which will require companies to pay a one-time transition tax on certain unrepatriated earnings from foreign subsidiaries. ASC 740, Income Taxes, requires a company to record the effects of a tax law change in the period of enactment. ASU 2018-05 allows a company to record a provisional amount when it does not have the necessary information available, prepared, or analyzed in reasonable detail to complete its accounting for the change in the tax law. The measurement period ends when the company has obtained, prepared, and analyzed the information necessary to finalize its accounting, but cannot extend beyond one year. We recorded income tax expense of $112.3 in the first six months of 2018, or 22.6% of earnings before income taxes. This amount reflects primarily two items: (1) The Tax Act resulted in a lower tax rate beginning in the first quarter of 2018. This includes the estimated impacts of requiring a current inclusion in U.S. federal income of certain earnings of controlled foreign corporations, allowing a domestic corporation an immediate deduction in the U.S. taxable income for a portion of its foreign derived intangible income, and the base erosion anti-abuse tax. These estimates had an immaterial impact on our effective income tax rate. (2) During the first quarter of 2018, we recorded a discrete income tax expense item which increased our estimated transition tax liability. During the second quarter of 2018, we recorded a discrete income tax benefit item related to the estimated impacts of accelerating depreciation for certain physical assets. These discrete items resulted in approximately $8.4 of income tax benefit during the first half of 2018. We will continue to monitor and evaluate guidance and clarifications from the Internal Revenue Service ('IRS') as it relates to the Tax Act and will refine these estimates as necessary. In general, it is our practice and intention to permanently reinvest the earnings of our foreign subsidiaries and repatriate earnings only when the tax impact is zero or very minimal and that position has not changed following incurring the transition tax under the Tax Act. No deferred taxes have been provided for withholding taxes or other taxes that would result upon repatriation of our foreign investments to the United States. It is not practicable to estimate the amount of deferred income tax liabilities related to investments in these foreign subsidiaries.

(4) Income Taxes

Fastenal files income tax returns in the United States federal jurisdiction, all states, and various local and foreign jurisdictions. With limited exceptions, we are no longer subject to income tax examinations by taxing authorities for taxable years before 2015 in the case of United States federal examinations, and 2013 in the case of foreign, state, and local examinations. During the first six months of 2018, there were no material changes in unrecognized tax benefits.

On December 22, 2017, the Tax Act was signed into law. The Tax Act made broad and complex changes to the U.S. tax code which include: a lowering of the U.S. federal corporate income tax rate from 35% to 21% effective January 1, 2018, accelerated expensing of qualified capital investments for a specific period, and a transition from a worldwide to a territorial tax system which will require companies to pay a one-time transition tax on certain unrepatriated earnings from foreign subsidiaries.

ASC 740, Income Taxes, requires a company to record the effects of a tax law change in the period of enactment. ASU 2018-05 allows a company to record a provisional amount when it does not have the necessary information available, prepared, or analyzed in reasonable detail to complete its accounting for the change in the tax law. The measurement period ends when the company has obtained, prepared, and analyzed the information necessary to finalize its accounting, but cannot extend beyond one year.

We recorded income tax expense of $112.3 in the first six months of 2018, or 22.6% of earnings before income taxes. This amount reflects primarily two items: (1) The Tax Act resulted in a lower tax rate beginning in the first quarter of 2018. This includes the estimated impacts of requiring a current inclusion in U.S. federal income of certain earnings of controlled foreign corporations, allowing a domestic corporation an immediate deduction in the U.S. taxable income for a portion of its foreign derived intangible income, and the base erosion anti-abuse tax. These estimates had an immaterial impact on our effective income tax rate. (2) During the first quarter of 2018, we recorded a discrete income tax expense item which increased our estimated transition tax liability. During the second quarter of 2018, we recorded a discrete income tax benefit item related to the estimated impacts of accelerating depreciation for certain physical assets. These discrete items resulted in approximately $8.4 of income tax benefit during the first half of 2018. We will continue to monitor and evaluate guidance and clarifications from the Internal Revenue Service ('IRS') as it relates to the Tax Act and will refine these estimates as necessary.

In general, it is our practice and intention to permanently reinvest the earnings of our foreign subsidiaries and repatriate earnings only when the tax impact is zero or very minimal and that position has not changed following incurring the transition tax under the Tax Act. No deferred taxes have been provided for withholding taxes or other taxes that would result upon repatriation of our foreign investments to the United States. It is not practicable to estimate the amount of deferred income tax liabilities related to investments in these foreign subsidiaries.