Segment Reporting (Schedule Of Identifiable Assets By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Stock option-based compensation costs	$ 86	$ 3
Subtotal	614,081		$ 607,556
General corporate	105,394		111,696
Cash and cash equivalents	36,135	$ 28,864	36,491	$ 29,511
Total assets	755,610		755,743
PE Films
Total assets	293,662		289,514
Flexible Packaging Films [Member] [Domain]
Total assets	47,810		49,915
Aluminum Extrusions
Total assets	$ 272,609		$ 268,127