Business Segments (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Thousands		3 Months Ended										12 Months Ended
		Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Total net sales	[1],[2]											$ 936,295		$ 1,029,444		$ 927,647
Goodwill, Impairment Loss												0		(46,792)		0
Total												74,284		41,439		(11,608)
Interest income												296		369		209
Interest expense												4,051		5,702		6,170
Gain (loss) on investment accounted for under the fair value method												10,900		30,600		33,800
Stock option-based compensation expense												4,209		1,221		264
Corporate expenses, net	[3]											36,630		28,893		30,879
Income (loss) before income taxes												58,172		36,368		(14,912)
Income tax expense (benefit)	[3]											9,913		11,526		(53,163)
Net income		$ (3,135)		$ 17,133	$ 14,477	$ 19,785	$ 26,157		$ (34,201)	$ 14,722	$ 18,165	48,259		24,842		38,251
Cash and cash equivalents		31,422	[1]				34,397	[1]				31,422	[1]	34,397	[1]	36,491	$ 29,511
Sales		232,427		$ 243,217	$ 248,248	$ 248,466	275,707		$ 267,294	$ 263,759	$ 258,711	972,358		1,065,471		961,330
Foreign Country
Revenue from External Customer [Line Items]
Cash and cash equivalents		23,000					31,100					23,000		31,100
Pension Benefits
Revenue from External Customer [Line Items]
Defined benefit pension plan net liability		$ (100,434)					$ (81,873)					(100,434)		(81,873)
kaleo
Revenue from External Customer [Line Items]
Gain (loss) on investment accounted for under the fair value method	[3]											28,482		30,600		33,800
Alleghany and Bath County, Virginia
Revenue from External Customer [Line Items]
Gain (loss) on investment accounted for under the fair value method												0		(186)		0
Gain (Loss) on Disposition of Assets												0		(38)		0
Unrealized Gain (Loss) on Investment Property												0		186		0
PE Films [Member]
Revenue from External Customer [Line Items]
Total net sales												272,758		332,488		352,459
segment EBITDA												37,803		51,058		55,889
Depreciation, Amortization and Accretion, Net												(14,627)		(14,877)		(14,343)
segment EBIT												23,176		36,181		41,546
Plant shutdowns, asset impairments, restructurings and other	[3]											(475)		(5,905)		(4,905)
Goodwill, Impairment Loss												0		46,792
Personal Care Materials [Member]
Revenue from External Customer [Line Items]
Goodwill, Impairment Loss												0		46,792
Aluminum Extrusions
Revenue from External Customer [Line Items]
Total net sales												529,602		573,126		466,833
segment EBITDA												65,683		65,479		58,524
Depreciation, Amortization and Accretion, Net												(16,719)		(16,866)		(15,070)
segment EBIT												48,964		48,613		43,454
Plant shutdowns, asset impairments, restructurings and other	[3]											(561)		(505)		321
Trade Name Accelerated Amortization												(10,040)		0		0
Goodwill, Impairment Loss												0
Flexible Packaging Films [Member] [Domain]
Revenue from External Customer [Line Items]
Total net sales												133,935		123,830		108,355
segment EBITDA												14,737		11,154		7,817
Depreciation, Amortization and Accretion, Net												(1,517)		(1,262)		(10,443)
segment EBIT												13,220		9,892		(2,626)
Plant shutdowns, asset impairments, restructurings and other	[3]											0		(45)		(89,398)
Shipping and Handling [Member]
Revenue from External Customer [Line Items]
Other Cost of Operating Revenue												36,063
Cost of Goods and Services Sold												$ 36,063		$ 36,027		$ 33,683

[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 $23.0 million and $31.1 million at December 31, 2019 and 2018, 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] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjQ4ZmFiYTVhZGM5MDRlMDZhZmZmMzZjZTZjMjVjMWM1fFRleHRTZWxlY3Rpb246NUZENkVBRjFFN0NFQzk2QjhFRTA2M0QxNDU5NUQ0QUYM}

[3] See Notes 1, 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.