Plants Shutdowns, Asset Impairments, Restructurings And Other (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended	18 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2016	Dec. 01, 2019	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Payments to Acquire Property, Plant, and Equipment			$ 14,528	$ 26,692
Production LIne Start-up and Ramp-up Costs	$ 1,500	$ 1,000	600	2,800
Asset impairments and costs associated with exit and disposal activities, net of adjustments	468	(271)	590	293
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	19,269	47,031	42,721	53,152
(Gain)/loss on asset impairments and divestitures			0	50
Other Non-Operating and Non-Recurring Charges [Abstract]
Unrealized gain (loss) on investment under fair value method			14,000	24,800
Gain (Loss) on Disposition of Assets			(109)	307
Payments for Restructuring			1,114
Restructuring Reserve	696		696				$ 1,103
kaleo
Other Non-Operating and Non-Recurring Charges [Abstract]
Unrealized gain (loss) on investment under fair value method	5,800	21,500	14,000	24,800
Unrealized gain (loss) on investment under fair value method, after taxes	4,500	15,700	$ 10,900	18,200
Fair Value Inputs, Discount Rate
Futura Industries [Member]
Restructuring Cost and Reserve [Line Items]
Net Business Combination Acquisition, Integration Costs and Other Related Costs				3,300
Business Combination, Inventory FV Adj				1,700
Business Combination, Acquisition Related Costs				1,500
Business Combination, Integration Related Costs				100
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Asset		(700)		(700)
Harbinger Capital Partners Special Situations Fund L P [Member]
Other Non-Operating and Non-Recurring Charges [Abstract]
Cost-method investment, OTTI	100		$ 100
Flexible Packaging Films [Member]
Restructuring Cost and Reserve [Line Items]
Businesss Combination Settlement of Escrow Account	0	(11,900)	0	(11,900)
Loss Contingency, Estimate of Possible Loss		3,500		3,500			3,500
PE Films
Restructuring Cost and Reserve [Line Items]
Production LIne Start-up and Ramp-up Costs		900		2,400
Pretax charges for severance and other employee-related costs		300		700
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other	(1,135)	(904)	(2,187)	(2,972)
Flexible Packaging Films [Member] [Domain]
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other	0	11,856	0	11,856
Aluminum Extrusions
Restructuring Cost and Reserve [Line Items]
Production LIne Start-up and Ramp-up Costs		100		400
Cast House Explosion pretax income		900		500
Cast House Explosion Excess Production Costs		600		600
Insured Event, Gain (Loss)		300
Loss from Catastrophes				100
Other Non-Operating and Non-Recurring Charges [Abstract]
Plant shutdowns, asset impairments, restructurings and other	(46)	1,571	(99)	(2,769)
Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Pretax charges for severance and other employee-related costs				300
Severance (a)
Other Non-Operating and Non-Recurring Charges [Abstract]
Payments for Restructuring			846
Restructuring Reserve	466		466				$ 627
Film Products Manufacturing Facility In Shanghai, China [Member] | Other Restructuring [Member] | PE Films
Restructuring Cost and Reserve [Line Items]
Asset impairments and costs associated with exit and disposal activities, net of adjustments	700		700
Pretax charges for severance and other employee-related costs	400
Accelerated Depreciation Expense	100
Restructuring and Disposal Activities - Anticipated Cash Cost Savings						$ 1,700
Other Restructuring Costs	200		200
Other Plant Consolidation Expenses - Cost of Goods Sold	100
Other Non-Operating and Non-Recurring Charges [Abstract]
Payments for Restructuring	100
Plant shutdowns, asset impairments, restructurings and other	600
Aluminum Extrusions Manufacturing Facility In Newnan Georgia [Member] | Aluminum Extrusions
Restructuring Cost and Reserve [Line Items]
Professional Fees	$ 300
Business Development Expenses		600		900
Other Non-Operating and Non-Recurring Charges [Abstract]
Environmental Exit Costs, Anticipated Cost				300
FilmProductsManufacturingFacilityInLakeZurichIllinois [Member] | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Tangible Asset Impairment Charges				100
Pretax charges for severance and other employee-related costs		300		100
Accelerated Depreciation Expense		100		200
Other Restructuring Costs		$ 200		400
Other Plant Consolidation Expenses - Cost of Goods Sold				$ 300
Pension Plan [Member]
Restructuring Cost and Reserve [Line Items]
Defined Benefit Plan Estimated Required Future Employer Contributions In Current Fiscal Year			$ 8,400
Restructuring Charges [Member] | Film Products Manufacturing Facility In Shanghai, China [Member] | Other Restructuring [Member] | PE Films
Restructuring Cost and Reserve [Line Items]
Pretax charges for severance and other employee-related costs						3,600
Accelerated Depreciation Expense						900
Other Restructuring Costs						2,400
Other Plant Consolidation Expenses - Cost of Goods Sold						1,100
Other Non-Operating and Non-Recurring Charges [Abstract]
Restructuring, Settlement and Impairment Provisions						$ 7,100