Segment Reporting Schedule of Revenue by Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Sales	$ 257,856	$ 238,500	$ 763,098	$ 690,654
UNITED STATES
Disaggregation of Revenue [Line Items]
Sales	176,022	150,154	506,769	434,766
PE Films
Disaggregation of Revenue [Line Items]
Sales	76,470	89,723	252,177	265,773
PE Films \| Personal Care Materials [Member]
Disaggregation of Revenue [Line Items]
Sales	57,356	63,574	174,985	187,661
PE Films \| Surface Protection Films [Member]
Disaggregation of Revenue [Line Items]
Sales	17,193	24,368	71,926	72,805
PE Films \| Films For Other Markets [Member]
Disaggregation of Revenue [Line Items]
Sales	1,921	1,781	5,266	5,307
PE Films \| Film Products Subtotal [Member]
Disaggregation of Revenue [Line Items]
Sales	76,470	89,723	252,177	265,773
Flexible Packaging Films [Member] [Domain]
Disaggregation of Revenue [Line Items]
Sales	33,725	26,628	90,466	79,925
Aluminum Extrusions
Disaggregation of Revenue [Line Items]
Sales	147,661	122,149	420,455	344,956
Aluminum Extrusions \| Nonresidential Building And Construction [Member]
Disaggregation of Revenue [Line Items]
Sales	75,870	63,187	213,500	177,534
Aluminum Extrusions \| Consumer Durables [Member]
Disaggregation of Revenue [Line Items]
Sales	14,991	14,105	47,300	39,871
Aluminum Extrusions \| Distribution [Member]
Disaggregation of Revenue [Line Items]
Sales	9,148	7,182	32,109	23,024
Aluminum Extrusions \| Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	13,205	9,682	33,992	29,947
Aluminum Extrusions \| Residential Building And Construction [Member]
Disaggregation of Revenue [Line Items]
Sales	11,163	10,327	32,976	29,855
Aluminum Extrusions \| Aluminum Extrusions Subtotal [Member]
Disaggregation of Revenue [Line Items]
Sales	147,661	122,149	420,455	344,956
Aluminum Extrusions \| Machinery and Equipment BNL [Domain]
Disaggregation of Revenue [Line Items]
Sales	11,191	8,430	30,335	23,975
Aluminum Extrusions \| Electrical [Member]
Disaggregation of Revenue [Line Items]
Sales	12,093	9,236	30,243	20,750
Exports From United States [Member] \| Asia [Member]
Disaggregation of Revenue [Line Items]
Sales	14,893	21,507	57,370	61,394
Exports From United States [Member] \| CANADA
Disaggregation of Revenue [Line Items]
Sales	13,451	11,253	40,988	35,855
Exports From United States [Member] \| Europe [Member]
Disaggregation of Revenue [Line Items]
Sales	1,608	2,193	5,127	6,826
Exports From United States [Member] \| Latin America [Member]
Disaggregation of Revenue [Line Items]
Sales	3,104	3,841	9,810	11,562
Operations Outside United States [Member] \| BRAZIL
Disaggregation of Revenue [Line Items]
Sales	26,591	22,030	73,402	64,682
Operations Outside United States [Member] \| NETHERLANDS
Disaggregation of Revenue [Line Items]
Sales	11,428	15,691	34,750	41,378
Operations Outside United States [Member] \| HUNGARY
Disaggregation of Revenue [Line Items]
Sales	7,987	6,331	25,324	17,660
Operations Outside United States [Member] \| CHINA
Disaggregation of Revenue [Line Items]
Sales	2,376	3,061	6,342	9,176
Operations Outside United States [Member] \| INDIA
Disaggregation of Revenue [Line Items]
Sales	$ 396	$ 2,439	$ 3,216	$ 7,355