Supplemental Cash Flow Information (Narrative) (Details) - USD ($)		12 Months Ended
Dec. 21, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net capital spending		$ 32,426,000	$ 34,436,000	$ 29,785,000
5.375% Senior Unsecured Note, Due January 2025 [Member]
Principal amount	$ 500,000,000	$ 500,000,000
Interest rate	5.375%	5.375%
Maturity date	Jan. 15, 2025	Jan. 15, 2025

Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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The net cash outflow or inflow from purchases, sales and disposals of property, plant and equipment and other productive assets, including intangibles.

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