Debt and Financing Arrangements (Details) $ / shares in Units, shares in Millions											9 Months Ended	12 Months Ended
	Feb. 08, 2024 USD ($)	Aug. 03, 2022 USD ($)	Jul. 29, 2021 USD ($) installment	Nov. 03, 2020 USD ($) $ / shares	Nov. 02, 2020 $ / shares	Nov. 01, 2020 shares	Oct. 29, 2020 USD ($) $ / shares	Jul. 02, 2020 USD ($)	Mar. 04, 2020 USD ($) installment	Mar. 07, 2017 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 31, 2018	Aug. 02, 2022 USD ($)	Mar. 04, 2021 USD ($)	Nov. 30, 2020 USD ($)
Debt Instrument [Line Items]
Term loan, face value																		$ 155,300,000
Interest rate																		5.25%
Restricted cash												$ 1,100,000	$ 1,100,000	$ 1,101,000
Debt financing costs												0.0	1,035,000	$ 2,057,000
Unamortized deferred financing fees												1,000,000.0	1,600,000
Outstanding debt												140,595,000	174,276,000
Derivative Assets												998,000	2,707,000
Paid-in Capital
Debt Instrument [Line Items]
Cash on convertible notes																		$ 39,200,000
Retained Earnings
Debt Instrument [Line Items]
Cash on convertible notes																		$ 6,700,000
Secured Debt | Subsequent Event
Debt Instrument [Line Items]
Term loan repaid	$ 3,500,000
New Term Loan Debt Facility | Senior Notes
Debt Instrument [Line Items]
Term loan, face value										$ 300,000,000
Percentage of face amount										99.50
Term loan repaid													273,800,000
Amount of voting equity interests of domestic subsidiaries guaranteed (percent)										100
Amount of voting equity interests of foreign owned subsidiaries guaranteed (percent)										65
Outstanding debt													6,500,000
Loss on Early Repayment of Debt													4,100,000
New Term Loan Debt Facility | Line of Credit | SOFR
Debt Instrument [Line Items]
Applicable margin on interest rate															2.75%
New Term Loan Debt Facility | Line of Credit | SOFR | Minimum
Debt Instrument [Line Items]
Applicable margin on interest rate															1.00%
New Term Loan Debt Facility | Line of Credit | Base Rate
Debt Instrument [Line Items]
Applicable margin on interest rate															1.75%
New senior secured term loan | Secured Debt | Subsequent Event
Debt Instrument [Line Items]
Term loan, face value	20,000,000.0
Amortization payments	$ 3,300,000
New Term Loan Debt Facility | Senior Notes
Debt Instrument [Line Items]
Quarterly principal amortization payments										$ 800,000
Mandatory prepayment amount (as percent)										100
Default to indebtedness										$ 50,000,000
Default to surety, reclamation, or similar bonds securing obligations										50,000,000
Default to uninsured judgment										50,000,000
Uninsured losses or proceedings against minimum amount										$ 50,000,000
Accounts Receivable Securitization Facility | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Current borrowing capacity												99,800,000
Letters of credit outstanding												50,200,000
Accounts Receivable Securitization Facility | Regions Bank | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Current borrowing capacity		$ 150,000,000														$ 110,000,000
Inventory-Based Revolving Credit Facility
Debt Instrument [Line Items]
Covenant amount												23,800,000
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Term loan, face value		$ 50
Letters of credit outstanding												$ 26,200,000
Borrowing base percentage, coal inventory		85
Borrowing base percentage, parts and supplies inventory		85
Borrowing base, percentage of clause		35
Percent of eligible cash		100.00%
Covenant amount											$ 100,000,000
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt | SOFR
Debt Instrument [Line Items]
Applicable margin on interest rate												0.75%
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt | SOFR | Minimum
Debt Instrument [Line Items]
Applicable margin on interest rate												2.25%
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt | SOFR | Maximum
Debt Instrument [Line Items]
Applicable margin on interest rate												3.50%
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt | Base Rate | Minimum
Debt Instrument [Line Items]
Applicable margin on interest rate												1.25%
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt | Base Rate | Maximum
Debt Instrument [Line Items]
Applicable margin on interest rate												2.50%
Equipment financing arrangement | Secured Debt
Debt Instrument [Line Items]
Term loan, face value			$ 23,500,000						$ 53,600,000
Number of monthly payments | installment			42						48
Interest rate			7.35%						6.34%
Tax Exempt Bonds
Debt Instrument [Line Items]
Term loan, face value												$ 98,100,000
Tax Exempt Bonds | Minimum
Debt Instrument [Line Items]
Covenant for cross-events of default to indebtedness											$ 50,000,000
Series 2020 Tax Exempt Bonds
Debt Instrument [Line Items]
Term loan, face value								$ 53,100,000
Interest rate								5.00%
Mandatory tender percentage								100.00%
Series 2021 Tax Exempt Bonds
Debt Instrument [Line Items]
Term loan, face value																	$ 45,000,000.0
Interest rate																	4.125%
Convertible Notes
Debt Instrument [Line Items]
Term loan, face value				$ 155,300,000
Interest rate				5.25%
Net proceeds of convertible debt				$ 132,700,000
Total interest expense													4,700,000
Contractual interest coupon													4,100,000
Amortization of debt discount													600,000
Principal amount of convertible notes												13,200,000	142,100,000
Cash on convertible notes												58,400,000	208,100,000
Deferred Offering Costs				$ 5,100,000
Unamortized Debt Issuance Expense													$ 3,800,000
Debt conversion, number of shares | shares													2.6
Loss on debt conversion												1,100,000	$ 10,300,000
Inducement premium payment													5,000,000.0
Professional fees													$ 1,500,000
Convertible Notes | Maximum
Debt Instrument [Line Items]
Total interest expense												100,000
Capped Call Transactions
Debt Instrument [Line Items]
Initial strike price (in dollars per share) | $ / shares				$ 37.325
Number of underlying shares | shares						4.2
Cap price | $ / shares					$ 52.255		$ 52.2550
Premium percentage (as percent)							75.00%
Capped call, transaction cost				$ 17,500,000			$ 17,500,000
Debt instrument capped call transaction intrinsic value												$ 62,100,000