Segment Reporting (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total net sales	$ 234,231	$ 257,856	$ 713,038	$ 763,098
Gross Sales	243,217	267,294	739,931	789,765
Goodwill, Impairment Loss	0	(46,792)	0	(46,792)
Goodwill, Impairment Loss, Net of Tax		38,200
Total Segment Income (Loss)	23,750	(29,960)	63,489	16,830
Interest income	56	6	163	290
Interest expense	859	1,318	3,354	4,539
Gain (loss) on investment in kaléo accounted for under fair value method			10,900	11,900
Gain (Loss) on Disposition of Assets			(6,328)	(86)
Cost-method Investments, Other than Temporary Impairment	0	186	0
Stock option-based compensation costs	807	415	2,121	806
Corporate expenses, net	9,350	6,926	26,840	21,668
Income from continuing operations before income taxes	17,090	(40,899)	59,819	1,821
Income taxes from continuing operations	(43)	(6,699)	8,424	3,135
Net income	17,133	(34,200)	51,395	(1,314)
kaleo
Segment Reporting Information [Line Items]
Gain (loss) on investment in kaléo accounted for under fair value method	4,300	(2,100)	28,482	11,900
PE Films
Segment Reporting Information [Line Items]
Total net sales	69,837	76,470	205,778	252,177
Operating profit from ongoing operations	6,889	4,145	17,606	26,857
Plant shutdowns, asset impairments, restructurings and other	3,834	(2,355)	933	(4,542)
Flexible Packaging Films [Member] [Domain]
Segment Reporting Information [Line Items]
Total net sales	34,888	33,725	101,950	90,466
Operating profit from ongoing operations	4,000	3,609	9,376	6,617
Plant shutdowns, asset impairments, restructurings and other	0	0	0	0
Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	129,506	147,661	405,310	420,455
Operating profit from ongoing operations	12,147	11,730	38,751	35,086
Plant shutdowns, asset impairments, restructurings and other	(610)	(297)	(667)	(396)
Accelerated Depreciation Expense	(2,510)	0	(2,510)	0
Alleghany and Bath County, Virginia [Member]
Segment Reporting Information [Line Items]
Cost-method Investments, Other than Temporary Impairment				186
Shipping and Handling [Member]
Segment Reporting Information [Line Items]
Cost of goods sold	8,986	9,438	26,893	26,667
Personal Care Materials [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	40,958	57,356	123,770	174,985
Surface Protection Films [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	27,052	17,193	76,194	71,926
Films For Other Markets [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	1,827	1,921	5,814	5,266
Film Products Subtotal [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	69,837	76,470	205,778	252,177
Nonresidential Building And Construction [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	64,341	75,870	202,998	213,500
Consumer Durables [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	12,939	14,991	44,865	47,300
Distribution [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	9,366	9,148	26,678	32,109
Automotive [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	11,091	13,205	36,214	33,992
Residential Building And Construction [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	11,110	11,163	33,060	32,976
Machinery and Equipment BNL [Domain] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	10,191	11,191	29,585	30,335
Electrical [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	10,468	12,093	31,910	30,243
Aluminum Extrusions Subtotal [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	129,506	147,661	405,310	420,455
Product [Member]
Segment Reporting Information [Line Items]
Cost of goods sold	$ 191,565	$ 217,378	$ 584,799	$ 631,235

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