Financial Instruments (Narrative) (Details) $ in Thousands, lb in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) lb	Dec. 31, 2017 USD ($) lb
Derivative [Line Items]
Net asset (liability)	$ (2,720)	$ (558)
Weight of aluminum that hedged future purchase of aluminum to meet fixed-price forward sales contract obligations, lbs | lb	22.5	8.0
Amounts of unrealized after-tax gains on derivative instruments	$ (1,100)
Aluminum Futures Contracts
Derivative [Line Items]
Notional amount	25,400	$ 8,200
Prepaid Expenses and Other Current Assets [Member] | Aluminum Futures Contracts
Derivative [Line Items]
Net asset (liability)	(1,630)
Cash Flow Hedging [Member] | Foreign Currency Forwwards And Options [Member]
Derivative [Line Items]
Foreign Currency Cash Flow Hedge Derivative at Fair Value, Net	900
Oct-2018 [Member] | Terphane Ltda [Member]
Derivative [Line Items]
Annual Net Costs Mismatch Translation Exposure - Real vs US Dollar	$ 125,000