Fair Value Measurements and Derivative Instruments - Fuel Price Risk (Details) - Fuel Swap Agreements $ in Millions		3 Months Ended
		Mar. 31, 2021 USD ($) T	Mar. 31, 2022 USD ($) T t	Dec. 31, 2021 USD ($) t T
Derivative Instruments
Discontinued cash flow hedge, nonmonetary amount | T		48,000
Estimated unrealized net loss associated with cash flow hedges pertaining to fuel swap agreements expected to be reclassified to earnings from accumulated other comprehensive income loss | $			$ 145.6	$ 23.8
Other income (expense)
Derivative Instruments
Reclassification | $		$ 4.4
2022
Derivative Instruments
Fuel Swap Agreements (metric tons) | T			660,650	821,850
Percentage of projected requirements			55.00%	54.00%
2022 | Not Designated as Hedging Instrument
Derivative Instruments
Discontinued cash flow hedge, nonmonetary amount			69,550
Fuel Swap Agreements (metric tons)	[1]		139,100	231,900
Notional amount since inception			69,550
2023
Derivative Instruments
Fuel Swap Agreements (metric tons) | T			249,050	249,050
Percentage of projected requirements			15.00%	15.00%
2023 | Not Designated as Hedging Instrument
Derivative Instruments
Fuel Swap Agreements (metric tons)			0	0

[1] As of March 31, 2022, 69,550 metric tons relate to fuel swap agreements with discontinued hedge accounting, in which we effectively pay fixed prices and receive floating prices from the counterparty. The remaining 69,550 tons relate to fuel swap agreements that were not designated as hedges since inception, in which we effectively pay floating prices and receive fixed prices from the counterparty.