Segment Reporting Schedule of Revenue by Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Sales	$ 177,917	$ 198,880	$ 543,544	$ 606,573
UNITED STATES
Disaggregation of Revenue [Line Items]
Sales	129,654	145,629	395,207	455,509
PE Films
Disaggregation of Revenue [Line Items]
Sales	26,440	34,487	103,444	99,313
PE Films \| Personal Care Materials [Member]
Disaggregation of Revenue [Line Items]
Sales	5,042	5,607	17,262	17,305
PE Films \| Surface Protection Films [Member]
Disaggregation of Revenue [Line Items]
Sales	19,868	27,053	79,919	76,194
PE Films \| Films For Other Markets [Member]
Disaggregation of Revenue [Line Items]
Sales	1,530	1,827	6,263	5,814
PE Films \| Film Products Subtotal [Member]
Disaggregation of Revenue [Line Items]
Sales	26,440	34,487	103,444	99,313
Flexible Packaging Films [Member] [Domain]
Disaggregation of Revenue [Line Items]
Sales	35,856	34,888	100,534	101,950
Aluminum Extrusions [Member]
Disaggregation of Revenue [Line Items]
Sales	115,621	129,505	339,566	405,310
Aluminum Extrusions [Member] \| Nonresidential Building And Construction [Member]
Disaggregation of Revenue [Line Items]
Sales	62,611	64,340	190,476	202,998
Aluminum Extrusions [Member] \| Consumer Durables [Member]
Disaggregation of Revenue [Line Items]
Sales	11,160	12,939	31,491	44,865
Aluminum Extrusions [Member] \| Distribution [Member]
Disaggregation of Revenue [Line Items]
Sales	7,796	9,366	22,055	26,678
Aluminum Extrusions [Member] \| Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	10,332	11,091	25,375	36,214
Aluminum Extrusions [Member] \| Residential Building And Construction [Member]
Disaggregation of Revenue [Line Items]
Sales	10,149	11,110	29,016	33,060
Aluminum Extrusions [Member] \| Aluminum Extrusions Subtotal [Member]
Disaggregation of Revenue [Line Items]
Sales	115,621	129,505	339,566	405,310
Aluminum Extrusions [Member] \| Machinery and Equipment BNL [Domain]
Disaggregation of Revenue [Line Items]
Sales	7,581	10,191	23,147	29,585
Aluminum Extrusions [Member] \| Electrical [Member]
Disaggregation of Revenue [Line Items]
Sales	5,992	10,468	18,006	31,910
Exports From United States [Member] \| Asia [Member]
Disaggregation of Revenue [Line Items]
Sales	14,255	23,163	59,816	61,037	$ 32,100
Revenues	5,900	8,600	25,100	21,300
Exports From United States [Member] \| CANADA
Disaggregation of Revenue [Line Items]
Sales	7,200	2,120	13,359	10,352
Exports From United States [Member] \| Europe [Member]
Disaggregation of Revenue [Line Items]
Sales	1,468	1,494	4,272	4,227
Exports From United States [Member] \| Latin America [Member]
Disaggregation of Revenue [Line Items]
Sales	465	880	1,953	1,359
Operations Outside United States [Member] \| BRAZIL
Disaggregation of Revenue [Line Items]
Sales	24,875	25,594	68,937	73,864
Operations Outside United States [Member] \| CHINA
Disaggregation of Revenue [Line Items]
Sales	$ 0	$ 0	$ 0	$ 225