Income Tax	6 Months Ended
Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Tax	Income Tax The Company’s 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 six months ended June 30, 2018 was 23% and 22%, respectively. Our tax rate for the second quarter of 2018 did not differ significantly from the combined federal and state statutory rate. The variance from the U.S. federal statutory tax rate of 21% for the first six months of 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 six months ended June 30, 2017 was 27% and 23%. 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. The Company continues to evaluate the impact of the U.S. Tax Cuts and Jobs Act (Tax Act) and has not adjusted its provisional tax estimates related to the Tax Act that it recorded in the fourth quarter of 2017. The Company's accounting remains incomplete as of June 30, 2018 and will be refined and, if necessary, adjusted throughout 2018 as required by SEC Staff Accounting Bulletin No. 118 (SAB 118).

Income Tax

The Company’s 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 six months ended June 30, 2018 was 23% and 22%, respectively. Our tax rate for the second quarter of 2018 did not differ significantly from the combined federal and state statutory rate. The variance from the U.S. federal statutory tax rate of 21% for the first six months of 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 six months ended June 30, 2017 was 27% and 23%. 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.

The Company continues to evaluate the impact of the U.S. Tax Cuts and Jobs Act (Tax Act) and has not adjusted its provisional tax estimates related to the Tax Act that it recorded in the fourth quarter of 2017. The Company's accounting remains incomplete as of June 30, 2018 and will be refined and, if necessary, adjusted throughout 2018 as required by SEC Staff Accounting Bulletin No. 118 (SAB 118).