Fair Value Measurements and Derivative Instruments - Balance Sheet (Details) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Asset Derivatives
Asset Derivatives		$ 82,499	$ 108,539
Liability Derivatives
Liability Derivatives		156,771	259,705
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	[1]	79,474	107,705
Liability Derivatives
Liability Derivatives	[1]	154,464	240,573
Notional Disclosures
Carrying Amount of the Hedged Liabilities		661,031	700,331
Cumulative amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Liabilities		12,514	17,512
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives		3,025	834
Liability Derivatives
Liability Derivatives		2,307	19,132
Interest rate swaps | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	[1]	12,433	17,271
Interest rate swaps | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	[1]	75	261
Liability Derivatives
Liability Derivatives	[1]	0	0
Interest rate swaps | Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives	[1]	101,306	144,653
Foreign currency forward contracts | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	[1]	3,831	20,836
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	[1]	18,132	63,894
Liability Derivatives
Liability Derivatives	[1]	49,408	13,294
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives	[1]	632	7,306
Foreign currency forward contracts | Not Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives		0	0
Liability Derivatives
Liability Derivatives		0	160
Fuel swaps | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	[1]	9,459	350
Fuel swaps | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	[1]	35,544	5,093
Liability Derivatives
Liability Derivatives	[1]	1,008	25,203
Fuel swaps | Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives	[1]	2,110	50,117
Fuel swaps | Not Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives		546	0
Fuel swaps | Not Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives		2,479	834
Liability Derivatives
Liability Derivatives		2,307	18,028
Fuel swaps | Not Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives		$ 0	$ 944

[1] Accounting Standard Codification 815-20 “Derivatives and Hedging.”