Principles Of Preparation (Supplemental Cash Flow Disclosures) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Supplemental Cash Flow Information [Abstract]
Interest on long-term debt and borrowings under the revolving credit facility	$ 11,967	$ 11,721
Proceeds from income tax refunds	(1,060)	(697)
Changes in accrued plant additions	(108)	(3,335)
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued	513	540
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued	$ 1,499	$ 932

(Increase) Decrease in capital expenditures incurred but not yet paid

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Amount of cash paid for interest. Includes, but is not limited to, payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

+ References

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The amount of cash received during the period as refunds for the overpayment of taxes.

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The fair value of stock issued in noncash financing activities.

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