|9 Months Ended|
Sep. 30, 2018
|Income Tax Disclosure [Abstract]|
|Income Tax||Income Tax
Our effective tax rate may vary from the U.S. federal statutory tax rate due to the change in the mix of earnings in various state jurisdictions with different statutory rates, benefits related to tax credits, and the tax impact of non-deductible expenses, stock award activities and other permanent differences between income before income taxes and taxable income. The effective tax rate for the three and nine months ended September 30, 2018 was 15% and 19%, respectively. The variance from the U.S. federal statutory tax rate of 21% for the three and nine months ended September 30, 2018 was primarily attributable to tax deductions related to stock award activities which were recorded as discrete items as well as the release of a valuation allowance relating to our investment in Viking. The effective tax rate for the three and nine months ended September 30, 2017 was 30% and 26%, respectively. The variance from the U.S. federal statutory tax rate of 35% was primarily attributable to tax deductions related to stock award activities which were recorded as discrete items in the quarter.
We continue to evaluate the impact of the U.S. Tax Cuts and Jobs Act (Tax Act) and have not adjusted our provisional tax estimates related to the Tax Act that it recorded in the fourth quarter of 2017. Our accounting remains incomplete as ofSeptember 30, 2018, and will be refined and, if necessary, adjusted by the end of 2018 as required by SEC Staff Accounting Bulletin No. 118 ("SAB 118").
The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef