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Plants Shutdowns, Asset Impairments, Restructurings And Other (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		18 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost and Reserve [Line Items]
Asset impairments and costs associated with exit and disposal activities, net of adjustments	$ 461	$ 1,056
Pretax charges for severance and other employee-related costs	175
(Gain) loss on asset impairments and divestitures	0	421
Other Restructuring Costs	47
Other Non-Operating and Non-Recurring Charges [Abstract]
Unrealized gain (loss) on investment under fair value method	26,100	(17,082)
Gain (Loss) on Disposition of Assets	0	(385)
Payments for Restructuring	(793)
Goodwill, Impairment Loss	13,696	0
Restructuring Reserve	809			$ 1,380
kaleo
Other Non-Operating and Non-Recurring Charges [Abstract]
Unrealized gain (loss) on investment under fair value method	(26,100)	17,082
Unrealized Gain Loss On Investments Net Of Tax	20,400	(14,300)
Other Interest and Dividend Income		17,600
PE Films
Other Non-Operating and Non-Recurring Charges [Abstract]
EBITDA	(906)	(1,378)
Aluminum Extrusions [Member]
Other Non-Operating and Non-Recurring Charges [Abstract]
Goodwill, Impairment Loss	(13,696)	0
EBITDA	(688)	$ (40)
Severance
Restructuring Cost and Reserve [Line Items]
Pretax charges for severance and other employee-related costs	47
Other Non-Operating and Non-Recurring Charges [Abstract]
Payments for Restructuring	28
Restructuring Reserve	748			$ 1,294
Personal Care Materials [Member] \| FilmProductsManufacturingFacilityInLakeZurichIllinois [Member] \| Other Restructuring [Member] \| PE Films
Restructuring Cost and Reserve [Line Items]
Other Restructuring Costs after Taxes	3,100
Pretax charges for severance and other employee-related costs	128		$ 1,100
Accelerated Depreciation Expense			1,700
Other Restructuring Costs	19		5,100
Other Plant Consolidation Expenses - Cost of Goods Sold			700
Other Non-Operating and Non-Recurring Charges [Abstract]
Restructuring, Settlement and Impairment Provisions			$ 6,900
Payments for Restructuring	$ 300