Other Events Narrative (Details) $ in Millions		3 Months Ended
	Apr. 16, 2024 USD ($)	Mar. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2023 AUD ($)
Other Commercial Events [Line Items]
Revenues		$ 983,600,000		$ 1,364,000,000
Other Noncash Income		9,800,000
Revenue from Collaborative Arrangement, Excluding Revenue from Contract with Customer					$ 30.0
Revenue related to excess port and rail capacity agreement		19,200,000
Common stock repurchase amount including commission fees		80,500,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 569,600,000
Stock Repurchased During Period, Shares | shares		3,200,000
Subsequent Event | Wards Well coal deposit
Other Commercial Events [Line Items]
Asset Acquisition, Price of Acquisition, Expected	$ 134,000,000
Contingent royalty	$ 200,000,000
Treasury Stock, Common
Other Commercial Events [Line Items]
Sales and Excise Tax Payable		$ 700,000		0
Unsettled common stock repurchases		(2,600,000)		$ 0
Accrued excise taxes related to common stock repurchases		4,000,000
North Antelope Rochelle Mine
Other Commercial Events [Line Items]
Storm Damage Provision		$ 1,800,000
Shoal Creek Mine
Other Commercial Events [Line Items]
Business interruption and property loss limits on insurance claim, amount			$ 125,000,000
Deductible amount			$ 50,000,000