Debt - Activity (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022	Apr. 30, 2021
Debt Instrument [Line Items]
Total debt	$ 512,000,000.0	$ 527,700,000
Industrial revenue bonds, variable
Debt Instrument [Line Items]
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly	$ 7,800,000	7,800,000
Maximum variable interest rate	12.00%
Effective interest rate	4.11%
Revolving credit facility | U.S. revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility	$ 68,200,000	90,000,000.0
Effective interest rate	9.25%
Revolving credit facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 0	35,000,000.0
Effective interest rate	8.40%
Casthouse Facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 3,100,000	0
Secured debt	86,200,000	49,400,000
Financing fees	$ 700,000
Effective interest rate	8.77%
Iceland term facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 4,800,000	13,300,000
Secured debt	0	1,200,000
Financing fees	$ 0
Stated interest rate, percentage	3.20%
Effective interest rate	6.88%
Vlissingen facility agreement | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 100,000	0
Secured debt	$ 10,000,000.0	0
Stated interest rate, percentage	8.75%
Senior secured notes, 7.5% | Senior notes
Debt Instrument [Line Items]
7.5% senior secured notes due April 1, 2028, net of financing fees of $2.8 million at September 30, 2023, interest payable semiannually	$ 247,200,000	246,600,000
Financing fees	$ 2,800,000
Stated interest rate, percentage	7.50%		7.50%
Senior convertible notes, 2.75% | Senior notes
Debt Instrument [Line Items]
2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.6 million at September 30, 2023, interest payable semiannually	$ 84,600,000	$ 84,400,000
Financing fees	$ 1,600,000
Stated interest rate, percentage	2.75%