Fair Value Measurements and Derivative Instruments - Fuel Price Risk (Details) - Fuel Swap Agreements $ in Millions		6 Months Ended
		Jun. 30, 2021 USD ($) T	Jun. 30, 2022 USD ($) 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 | $			$ 149.9	$ 23.8
2022
Derivative Instruments
Fuel Swap Agreements (metric tons) | T			453,450	821,850
Percentage of projected requirements			56.00%	54.00%
2022 | Not Designated as Hedging Instrument
Derivative Instruments
Discontinued cash flow hedge, nonmonetary amount			55,250
Fuel Swap Agreements (metric tons)	[1]		110,500	231,900
Notional amount since inception			55,250
2023
Derivative Instruments
Fuel Swap Agreements (metric tons) | T			415,750	249,050
Percentage of projected requirements			26.00%	15.00%
2023 | Not Designated as Hedging Instrument
Derivative Instruments
Fuel Swap Agreements (metric tons)			0	0
Other Income (Expense)
Derivative Instruments
Reclassification | $		$ 4.4

[1] As of June 30, 2022, 55,250 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 55,250 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.