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Segment Reporting (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 690,936		$ 690,936		$ 755,743
Total net sales	257,856	$ 238,500	763,098	$ 690,654
Gross Sales	267,294	247,121	789,765	715,494
Goodwill, Impairment Loss	(46,792)	0	(46,792)	0
Total Segment Income (Loss)	(29,960)	21,482	16,830	66,593
Interest income	6	42	290	171
Interest expense	1,318	1,757	4,539	4,579
Gain (loss) on investment in kaléo accounted for under fair value method			11,900	24,800
Gain (Loss) on Disposition of Assets			(86)	412
Cost-method Investments, Other than Temporary Impairment	(186)	0	(186)
Stock option-based compensation costs	415	111	806	153
Corporate expenses, net	6,926	6,960	21,668	20,985
Income from continuing operations before income taxes	(40,899)	12,696	1,821	65,847
Income taxes from continuing operations	(6,699)	4,422	3,135	9,667
Net income	(34,200)	8,274	(1,314)	56,180
kaleo
Segment Reporting Information [Line Items]
Gain (loss) on investment in kaléo accounted for under fair value method	(2,100)	0	11,900	24,800
PE Films
Segment Reporting Information [Line Items]
Assets	231,106		231,106		289,514
Total net sales	76,470	89,723	252,177	265,773
Operating profit from ongoing operations	4,145	11,251	26,857	30,965
Plant shutdowns, asset impairments, restructurings and other	(2,355)	(919)	(4,542)	(3,890)
Flexible Packaging Films [Member] [Domain]
Segment Reporting Information [Line Items]
Assets	53,661		53,661		49,915
Total net sales	33,725	26,628	90,466	79,925
Operating profit from ongoing operations	3,609	(1,074)	6,617	(3,392)
Plant shutdowns, asset impairments, restructurings and other	0	0	0	11,856
Aluminum Extrusions
Segment Reporting Information [Line Items]
Assets	277,810		277,810		$ 268,127
Total net sales	147,661	122,149	420,455	344,956
Operating profit from ongoing operations	11,730	12,601	35,086	34,201
Plant shutdowns, asset impairments, restructurings and other	(297)	(377)	(396)	(3,147)
Alleghany and Bath County, Virginia [Member]
Segment Reporting Information [Line Items]
Cost-method Investments, Other than Temporary Impairment				0
Shipping and Handling [Member]
Segment Reporting Information [Line Items]
Freight	9,438	8,621	26,667	24,840
Personal Care Materials [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	57,356	63,574	174,985	187,661
Surface Protection Films [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	17,193	24,368	71,926	72,805
Films For Other Markets [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	1,921	1,781	5,266	5,307
Film Products Subtotal [Member] \| PE Films
Segment Reporting Information [Line Items]
Total net sales	76,470	89,723	252,177	265,773
Nonresidential Building And Construction [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	75,870	63,187	213,500	177,534
Consumer Durables [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	14,991	14,105	47,300	39,871
Distribution [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	9,148	7,182	32,109	23,024
Automotive [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	13,205	9,682	33,992	29,947
Residential Building And Construction [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	11,163	10,327	32,976	29,855
Machinery and Equipment BNL [Domain] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	11,191	8,430	30,335	23,975
Electrical [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	12,093	9,236	30,243	20,750
Aluminum Extrusions Subtotal [Member] \| Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	147,661	122,149	420,455	344,956
Product [Member]
Segment Reporting Information [Line Items]
Freight	$ 217,378	$ 194,508	$ 631,235	$ 569,555