Derivatives and Financial Instruments - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) T	Dec. 31, 2017 USD ($) T	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Derivative financial liabilities	$ 0
Derivative loss deferred in equity	400,000	$ 700,000	$ 3,100,000
Derivative (loss) gain transferred to consolidated income statement	$ (100,000)	$ 600,000	$ (900,000)
Primary aluminum purchased during period, mass | T	11,500	12,500
Overdrafts	$ 3,500,000	$ 4,200,000
Long-term debt outstanding	77,100,000	113,800,000
Debt issuance costs	$ 1,400,000	$ 1,700,000
LME derivative contract
Derivative [Line Items]
Percentage of primary aluminum requirement hedged by LME derivatives	0.00%	32.00%
Derivative, nonmonetary notional amount, mass | T	3,300	3,000
Increase in cost per $100 increase in LME price of aluminum	$ 1,100,000
Accounts and Other Receivables
Derivative [Line Items]
Derivative financial assets	100,000	$ 2,100,000
Other Non-current Assets
Derivative [Line Items]
Derivative financial assets	0	300,000
Other Current Liabilities
Derivative [Line Items]
Derivative financial liabilities		1,500,000
Other Noncurrent Liabilities
Derivative [Line Items]
Derivative financial liabilities		400,000
Bank and other loans
Derivative [Line Items]
Long-term debt outstanding	75,000,000	111,300,000
Debt issuance costs	1,400,000	1,700,000
Variable interest rate debt	$ 0	$ 21,300,000