Debt and Financing Arrangements (Company Debt Narrative) (Details) $ / shares in Units, shares in Millions										3 Months Ended		12 Months Ended
	Jul. 29, 2021 USD ($) installment	Nov. 03, 2020 USD ($) $ / shares shares	Oct. 29, 2020 $ / shares	Sep. 30, 2020 USD ($)	Sep. 29, 2020 USD ($)	Sep. 28, 2020 USD ($)	Jul. 02, 2020 USD ($)	Mar. 04, 2020 USD ($) installment	Mar. 07, 2017 USD ($)	Mar. 31, 2022 USD ($) item $ / shares	Mar. 31, 2021 USD ($)	Dec. 31, 2018	Dec. 31, 2021 USD ($)	Mar. 04, 2021 USD ($)	Nov. 30, 2020 USD ($)
Debt Instrument [Line Items]
Term loan, face value		$ 155,300,000								$ 155,300,000					$ 155,300,000
Letters of credit outstanding										95,300,000
Interest rate		5.25%													5.25%
Restricted Cash										1,100,000	$ 18,962,000		$ 1,101,000
Derivative liabilities										12,838,000			2,203,000
Debt financing costs											1,194,000
Equity components liability of the convertible notes										114,500,000
Equity components of the convertible notes										40,800,000
Long-term Debt										314,901,000			560,673,000
Unamortized Debt Issuance Expense										4,400,000
Paid-in Capital
Debt Instrument [Line Items]
Equity components of the convertible notes		$ 39,200,000													$ 39,200,000
Retained Earnings
Debt Instrument [Line Items]
Equity components of the convertible notes		6,700,000													$ 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										271,500,000
Amount of voting equity interests of domestic subsidiaries guaranteed (percent)									100
Amount of voting equity interests of foreign owned subsidiaries guaranteed (percent)									65
Long-term Debt										8,800,000
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]
Derivative liabilities										300,000
Gain (loss) on interest rate swap										100,000
Amount reclassified from other comprehensive income to expense		1,400,000
Accounts Receivable Securitization Facility | Line of Credit | Secured Debt
Debt Instrument [Line Items]
Current borrowing capacity										42,400,000
Letters of credit outstanding										67,600,000
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
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	$ 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
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								$ 37.126
Stock price trigger (as a percent)										130.00%
Trading days, number | item										20
Convertible Notes exceeded the principal amount										$ 419,200,000
Consecutive trading days, period | item										30
Total interest expense										$ 2,300,000	3,700,000
Contractual interest coupon										2,000,000.0	2,000,000.0
Amortization of debt discount										$ 300,000	$ 1,700,000
Deferred Offering Costs		$ 5,100,000
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
Capped call, transaction cost		$ 17,500,000