Derivative Financial Instruments (Narrative) (Details) R$ in Thousands, $ in Thousands, lb in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) lb	Mar. 31, 2017 lb	Mar. 31, 2018 BRL (R$)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Amounts of unrealized after tax gains (losses) to be Reclassified within Twelve Months	$ (100)
Aluminum Futures Contracts
Derivative [Line Items]
Notional Amount				$ 17,700	$ 8,200
Weight of aluminum that hedged future purchase of aluminum to meet fixed - price forward sales contract obligations, lbs | lb	18.2	8.0
Net asset (liability), Fair Value				(62)	562
Accrued Expenses [Member] | Derivatives Designated As Hedging Instruments [Member] | Aluminum Futures Contracts
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset				491	578
Derivative Liability, Fair Value, Gross Liability				553	$ 16
Cost of Sales [Member] | Foreign Currency Forwards And Options [Member]
Derivative [Line Items]
Notional Amount			R$ 48,500	$ 15,000