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Debt - Credit Facility (Details)	Apr. 29, 2019 USD ($) payment	Jul. 01, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2013 USD ($)
Line of Credit Facility [Line Items]
Fair value of debt instrument			$ 250,500,000	$ 244,200,000
U.S. revolving credit facility [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings			45,000,000.0
Credit facility maximum amount			175,000,000.0
Borrowing availability			106,200,000
Borrowing availability, net of outstanding letters of credit and borrowings			42,900,000
Borrowing availability, net of borrowings			18,300,000
U.S. revolving credit facility [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility face amount			175,000,000.0
U.S. letter of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount			110,000,000.0
U.S. revolving credit facility, accordion [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility face amount			50,000,000.0
Iceland revolving line of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings			45,000,000.0
Credit facility maximum amount			50,000,000.0
Borrowing availability			50,000,000.0
Borrowing availability, net of outstanding letters of credit and borrowings			0
Borrowing availability, net of borrowings			$ 5,000,000.0
Senior secured notes due June 01, 2021 [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Face amount					$ 250,000,000.0
Stated interest rate, percentage					7.50%
Senior secured notes due 2025 [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Face amount		$ 250,000,000
Senior secured notes due 2025 [Member] | Long-term Debt [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Face amount		$ 250,000,000.0
Interest rate, cash percentage		10.00%
Interest rate, additional notes or cash percentage		2.00%
Revolving credit facility [Member] | Iceland revolving line of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Stated interest rate, percentage			3.80%
Revolving credit facility			$ 45,000,000.0	$ 0
Short-term Debt [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Stated interest rate, percentage			5.375%
Short-term Debt [Member] | Revolving credit facility [Member] | U.S. revolving credit facility [Member]
Line of Credit Facility [Line Items]
Stated interest rate, percentage			2.50%
Debt, financial covenant, fixed coverage ratio			1.0
Debt, financial covenant, amount			$ 17,500,000
Debt, financial covenant, borrowing base, percentage			10.00%
Debt, financial covenant, borrowing base, minimum			$ 12,500,000
Hawesville [Member]
Line of Credit Facility [Line Items]
Due to related parties, noncurrent	$ 40,000,000.0
Debt instrument, payment terms, number of monthly payments | payment	24
London Interbank Offered Rate (LIBOR) [Member] | Hawesville [Member]
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	5.375%

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Debt, Financial Covenant, Amount

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Debt, Financial Covenant, Fixed Coverage Ratio

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Debt Instrument, Interest Rate, Stated Percentage, Additional Notes or Cash

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Debt Instrument, Payment Terms, Number of Monthly Payments

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The amount of additional borrowings provided in credit facility under a letter of credit sub-facility.

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Line of Credit Facility, Remaining Borrowing Capacity, Net of Letters of Credit

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Carrying amount as of the balance sheet date of obligations due all related parties.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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