Segment Reporting (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 754,489		$ 754,489		$ 755,743
Total net sales	255,319	$ 239,435	505,241	$ 452,154
Add back freight	8,440	7,912	17,229	16,218
Sales as shown in the Consolidated Statements of Income	263,759	247,347	522,470	468,372
Total Segment Income (Loss)	21,947	34,658	46,789	45,112
Interest income	228	55	284	129
Interest expense	1,577	1,642	3,221	2,822
Gain (loss) on investment in kaléo accounted for under fair value method			14,000	24,800
Gain (Loss) on Disposition of Assets			(109)	307
Stock option-based compensation costs	305	38	391	41
Corporate expenses, net	6,824	7,502	14,740	14,026
Income from continuing operations before income taxes	19,269	47,031	42,721	53,152
Income taxes from continuing operations	4,547	2,827	9,834	5,246
Net income	14,722	44,204	32,887	47,906
kaleo
Segment Reporting Information [Line Items]
Gain (loss) on investment in kaléo accounted for under fair value method	5,800	21,500	14,000	24,800
PE Films
Segment Reporting Information [Line Items]
Assets	283,536		283,536		289,514
Total net sales	82,457	89,639	175,707	176,050
Operating profit from ongoing operations	8,678	10,682	22,712	19,713
Plant shutdowns, asset impairments, restructurings and other	(1,135)	(904)	(2,187)	(2,972)
Flexible Packaging Films [Member] [Domain]
Segment Reporting Information [Line Items]
Assets	48,845		48,845		49,915
Total net sales	28,304	26,588	56,741	53,297
Operating profit from ongoing operations	1,294	(319)	3,008	(2,317)
Plant shutdowns, asset impairments, restructurings and other	0	11,856	0	11,856
Aluminum Extrusions
Segment Reporting Information [Line Items]
Assets	274,577		274,577		$ 268,127
Total net sales	144,558	123,208	272,793	222,807
Operating profit from ongoing operations	13,156	11,772	23,355	21,601
Plant shutdowns, asset impairments, restructurings and other	(46)	1,571	(99)	(2,769)
Personal Care Materials [Member] | PE Films
Segment Reporting Information [Line Items]
Total net sales	55,985	62,790	117,629	124,088
Surface Protection Films [Member] | PE Films
Segment Reporting Information [Line Items]
Total net sales	24,918	24,996	54,733	48,437
Films For Other Markets [Member] | PE Films
Segment Reporting Information [Line Items]
Total net sales	1,555	1,853	3,345	3,526
Film Products Subtotal [Member] | PE Films
Segment Reporting Information [Line Items]
Total net sales	82,458	89,639	175,707	176,051
Nonresidential Building And Construction [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	72,442	61,173	137,629	114,347
Consumer Durables [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	17,161	14,024	32,309	25,766
Distribution [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	12,031	9,408	22,961	15,842
Automotive [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	11,157	10,112	20,787	20,265
Residential Building And Construction [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	12,343	13,068	21,813	19,528
Machinery and Equipment BNL [Domain] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	9,867	8,606	19,144	15,545
Electrical [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	9,556	6,817	18,150	11,513
Aluminum Extrusions Subtotal [Member] | Aluminum Extrusions
Segment Reporting Information [Line Items]
Total net sales	$ 144,557	$ 123,208	$ 272,793	$ 222,806