Plants Shutdowns, Asset Impairments, Restructurings And Other (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		16 Months Ended	18 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Asset impairments and costs associated with exit and disposal activities, net of adjustments	$ 1,464	$ 1,209	$ 3,595	$ 1,799
(Gain)/loss on asset impairments and divestitures			519	185
Other Non-Operating and Non-Recurring Charges [Abstract]
Unrealized gain (loss) on investment under fair value method			(10,900)	(11,900)
Cost-method investment, OTTI	0	(186)	0
Gain (Loss) on Disposition of Assets			(6,328)	(86)
Payments for Restructuring			(1,933)
Goodwill, Impairment Loss	0	46,792	0	46,792
Restructuring Reserve	1,563		1,563		$ 1,563		$ 776
kaleo
Other Non-Operating and Non-Recurring Charges [Abstract]
Unrealized gain (loss) on investment under fair value method	(4,300)	2,100	(28,482)	(11,900)
Unrealized Gain Loss On Investments Net Of Tax	3,400		23,400
Other Interest and Dividend Income			17,582
PE Films
Restructuring Cost and Reserve [Line Items]
Pretax charges for severance and other employee-related costs	100		600
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other	3,834	(2,355)	933	(4,542)
Flexible Packaging Films [Member] [Domain]
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other	0	0	0	0
Aluminum Extrusions
Restructuring Cost and Reserve [Line Items]
Accelerated Depreciation Expense	(2,510)	0	(2,510)	0
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other	(610)	(297)	(667)	(396)
Severance
Restructuring Cost and Reserve [Line Items]
Pretax charges for severance and other employee-related costs			2,043
Other Non-Operating and Non-Recurring Charges [Abstract]
Payments for Restructuring			(1,212)
Restructuring Reserve	1,447		1,447		1,447		$ 616
Film Products Manufacturing Facility In Shanghai, China [Member]
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other			6,300
Film Products Manufacturing Facility In Shanghai, China [Member] | Other Restructuring [Member] | PE Films
Restructuring Cost and Reserve [Line Items]
Other Restructuring Costs after Taxes					4,000
Pretax charges for severance and other employee-related costs			101
Other Restructuring Costs			600
Other Non-Operating and Non-Recurring Charges [Abstract]
Gain (Loss) on Disposition of Assets	6,316	$ 0	6,316	0
Payments for Restructuring	200		700		$ 3,200
Alleghany and Bath County, Virginia [Member]
Other Non-Operating and Non-Recurring Charges [Abstract]
Cost-method investment, OTTI				$ (186)
PE Films | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Pretax charges for severance and other employee-related costs			628
Personal Care Materials [Member] | PE Films Products Manufacturing Facility Restag Hungary [Domain] | Other Restructuring [Member] | PE Films
Other Non-Operating and Non-Recurring Charges [Abstract]
Inventory Write-down	200
Personal Care Materials [Member] | FilmProductsManufacturingFacilityInLakeZurichIllinois [Member] | Other Restructuring [Member] | PE Films
Restructuring Cost and Reserve [Line Items]
Other Restructuring Costs after Taxes	1,900
Pretax charges for severance and other employee-related costs			720			$ 1,800
Accelerated Depreciation Expense						1,600
Losses Associated With Plant Shutdowns Asset Impairments Restructurings Unusual Items Gains Losses From Sale Of Assets Other Items						5,000
Other Restructuring Costs			0			5,100
Other Plant Consolidation Expenses - Cost of Goods Sold						700
Other Non-Operating and Non-Recurring Charges [Abstract]
Restructuring, Settlement and Impairment Provisions						7,600
Payments for Restructuring	200		200
Personal Care Materials [Member] | PE Films Personal Care European Operations [Member] | Other Restructuring [Member] | PE Films
Restructuring Cost and Reserve [Line Items]
Other Restructuring Costs after Taxes	700
Pretax charges for severance and other employee-related costs			594
Other Restructuring Costs			$ 0
Other Non-Operating and Non-Recurring Charges [Abstract]
Restructuring, Settlement and Impairment Provisions						$ 1,700
Payments for Restructuring	100
Personal Care Materials [Member] | Films Products Manufacturing Facility Guangzhou China [Domain] | Other Restructuring [Member] | PE Films
Other Non-Operating and Non-Recurring Charges [Abstract]
Impairment of Long-Lived Assets to be Disposed of	$ 400