Debt and Financing Arrangements (Company Debt Narrative) (Details) $ / shares in Units, shares in Millions									1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2022 USD ($) shares	Jul. 29, 2021 USD ($) installment	Nov. 03, 2020 USD ($) $ / shares shares	Oct. 29, 2020 $ / shares	Sep. 30, 2020 USD ($)	Jul. 02, 2020 USD ($)	Mar. 04, 2020 USD ($) installment	Mar. 07, 2017 USD ($)	Aug. 31, 2020 USD ($)	Jun. 30, 2022 USD ($) item $ / shares	Mar. 31, 2022 USD ($)	Jun. 30, 2022 USD ($) $ / shares	Jun. 30, 2021 USD ($)	Dec. 31, 2018	Dec. 31, 2021 USD ($)	Mar. 04, 2021 USD ($)	Nov. 30, 2020 USD ($)	Sep. 29, 2020 USD ($)
Debt Instrument [Line Items]
Term loan, face value																	$ 155,300,000
Letters of credit outstanding										$ 94,800,000		$ 94,800,000
Interest rate																	5.25%
Restricted cash										1,100,000		1,100,000	$ 7,104,000		$ 1,101,000
Debt financing costs													$ 1,537,000
Outstanding debt										183,027,000		183,027,000			560,673,000
Derivative Assets										11,435,000		11,435,000			6,104,000
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
New Term Loan Debt Facility | Senior Notes
Debt Instrument [Line Items]
Term loan, face value								$ 300,000,000
Percentage of face amount								99.50
Quarterly principal amortization payments								$ 750,000
Term loan repaid												272,300,000
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										8,000,000.0		8,000,000.0
Loss on Early Repayment of Debt												4,100,000
New Term Loan Debt Facility | Line of Credit | LIBOR
Debt Instrument [Line Items]
Applicable margin on interest rate														2.75%
New Term Loan Debt Facility | Line of Credit | LIBOR | 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%
Interest Rate Swap
Debt Instrument [Line Items]
Gains on interest rate swap										700,000
Amount reclassified from other comprehensive income to expense											$ 1,400,000
Derivative Assets										800,000		800,000
Accounts Receivable Securitization Facility | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Current borrowing capacity										42,900,000		42,900,000
Letters of credit outstanding										67,100,000		67,100,000
Accounts Receivable Securitization Facility | Regions Bank | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Current borrowing capacity					$ 110,000,000													$ 160,000,000
Inventory-Based Revolving Credit Facility
Debt Instrument [Line Items]
Covenant amount												22,300,000
Inventory-Based Revolving Credit Facility | Regions Bank | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Term loan, face value					$ 50,000,000
Letters of credit outstanding										27,700,000		27,700,000
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				$ 175,000,000
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		$ 98,100,000			$ 98,100,000
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
Initial Conversion ratio			0.267917
Initial Conversion price (in dollars per share) | $ / shares			$ 37.325							$ 35.448		$ 35.448
Stock price trigger (as a percent)										130.00%
Trading days, number | item										20
Convertible Notes exceeded the principal amount												$ 91,100,000
Consecutive trading days, period | item										30
Total interest expense										$ 1,600,000		4,000,000.0
Contractual interest coupon										1,400,000		3,500,000
Amortization of debt discount										200,000		500,000
Principal amount of convertible notes	$ 125,200,000
Cash on convertible notes	130,100,000
Deferred Offering Costs			$ 5,100,000
Unamortized deferred financing fees										3,400,000		3,400,000
Outstanding debt	$ 30,000,000									30,100,000		30,100,000
Debt conversion, number of shares | shares	2.6
Loss on debt conversion										9,600,000
Inducement premium payment										4,700,000
Professional fees										1,500,000
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
Capped call, transaction cost			$ 17,500,000
Debt instrument capped call transaction intrinsic value										$ 62,100,000		$ 62,100,000