Business Segments (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Cost of Goods and Services Sold		$ 849,756	$ 767,550	$ 659,867
Net Sales	[1],[2]	1,029,444	927,647	799,272
PE Films [Member]
Segment Reporting Information [Line Items]
Net Sales		332,488	352,459	331,146
PE Films [Member] | The Procter And Gamble Company
Segment Reporting Information [Line Items]
Net Sales		106,500	122,400	129,100
Shipping and Handling [Member]
Segment Reporting Information [Line Items]
Cost of Goods and Services Sold		$ 36,027	$ 33,683	$ 29,069

[1] Information on exports and foreign operations are provided on the previous page. Cash and cash equivalents includes funds held in locations outside the U.S. of $31.1 million and $32.7 million at December 31, 2018 and 2017, respectively. Export sales relate almost entirely to PE Films. Operations outside the U.S. in The Netherlands, Hungary, China and India also relate to PE Films. Operations in Brazil are primarily related to Flexible Packaging Films, but also include PE Films operations. Sales from locations in The Netherlands and Hungary are primarily to customers located in Europe. Sales from locations in China (Guangzhou and Shanghai) are primarily to customers located in China, but also include other customers in Asia.

[2] The difference between total consolidated sales as reported in the consolidated statements of income and segment, geographic and product group net sales reported in this note is freight of $36.0 million in 2018, $33.7 million in 2017 and $29.1 million in 2016.