6.	Income Taxes

The Corporation’s effective income tax rate for the three months ended March 31, 2017 was 25.6%. The effective income tax rate reflects the effect of federal and state income taxes and the impact of differences in book and tax accounting arising from the net permanent benefits associated with the statutory depletion deduction for mineral reserves and the domestic production deduction. For the three months ended March 31, 2017, as a result of the adoption of ASU 2016-09 (see Note 1), the effective income tax rate reflects the excess tax benefit related to the vesting and exercise of stock-based compensation awards, which are treated as discrete events. As previously stated in Note 1, this requirement of the ASU is prospective and therefore, prior year results are not comparable.

The Corporation records interest accrued in relation to unrecognized tax benefits as income tax expense. Penalties, if incurred, are recorded as operating expenses in the consolidated statements of earnings and comprehensive earnings.