Investments (Schedule Of Fair Value Method Investments, Balance Sheets And Income Statements) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents		$ 11,846				$ 31,422				$ 11,846	$ 31,422	$ 34,397	$ 36,491
Net property, plant and equipment		166,545				173,556				166,545	173,556
Patents		18,820				22,636				18,820	22,636
Other assets		3,506				4,628				3,506	4,628
Total assets	[1]	514,870				712,668				514,870	712,668
Liabilities and Shareholders’ Equity
Other noncurrent liabilities		134,000				42,000				134,000	42,000
Equity		109,055				376,749				109,055	376,749	354,857	$ 343,780
Total liabilities and shareholders’ equity		514,870				712,668				514,870	712,668
Revenues & Expenses:
Cost of goods sold										(558,967)	(641,140)	(679,665)
Income tax (expense) benefit	[2]									8,213	(13,545)	(18,807)
Net income (loss)		$ 895	$ (65,213)	$ 11,196	$ (22,321)	$ (3,136)	$ 17,133	$ 14,477	$ 19,785	$ (75,444)	$ 48,259	$ 24,842

[1] Cash and cash equivalents includes funds held in locations outside the U.S. of $9.4 million and $8.9 million at December 31, 2020 and 2019, respectively. (c)Information on exports and foreign operations are provided on the previous page. Export sales relate almost entirely to PE Films. Operations in China relate to PE Films. Operations in Brazil relate to Flexible Packaging Films.

[2] See Notes 1, 2, 3, 4 and 17 for more information on losses associated with plant shutdowns, asset impairments and restructurings, unusual items, gains or losses from sale of assets, gains or losses on an investment accounted for under the fair value method and other items.