Income Taxes	3 Months Ended
Mar. 31, 2018
Income Taxes [Abstract]
Income Taxes	(10)INCOME TAXES For interim period reporting, we record income taxes using an estimated annual effective tax rate based upon projected annual income, forecasted permanent tax differences, discrete items and statutory rates in states in which we operate. Our effective tax rate for the three months ended March 31, 2018 and March 31, 2017 was 7% and 8%, respectively. Historically, our actual effective tax rates have differed from the statutory effective rate primarily due to the benefit received from statutory percentage depletion deductions. The deduction for statutory percentage depletion does not necessarily change proportionately to changes in income before income taxes.

Income Taxes

3 Months Ended

Mar. 31, 2018

(10)INCOME TAXES

For interim period reporting, we record income taxes using an estimated annual effective tax rate based upon projected annual income, forecasted permanent tax differences, discrete items and statutory rates in states in which we operate. Our effective tax rate for the three months ended March 31, 2018 and March 31, 2017 was 7% and 8%, respectively. Historically, our actual effective tax rates have differed from the statutory effective rate primarily due to the benefit received from statutory percentage depletion deductions. The deduction for statutory percentage depletion does not necessarily change proportionately to changes in income before income taxes.