Long-term Debt (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Current portion of long-term debt	$ 446,924	$ 442,360
Current portion of unamortized debt issue cost, net	(3,738)	(3,858)
Current portion of long-term debt, net of debt issue costs	443,186	438,502
Long-term debt, net of current maturities	2,655,391	2,966,951
Long-term portion of unamortized debt issue cost, net	(21,684)	(25,179)
Long-term debt, net of current maturities and debt issue costs	2,633,707	2,941,772
Total long-term debt (including current portion)	3,102,315	3,409,311
Total unamortized debt issue cost, net	(25,422)	(29,037)
Total long-term debt, net of debt issue costs	$ 3,076,893	3,380,274
Effective interest rate (as a percent)	4.10%
Letters of credit and surety bonds
Debt Instrument [Line Items]
Letters of credit and surety bonds outstanding with various banks and surety institutions	$ 50,800	$ 59,200
Letters of credit
Debt Instrument [Line Items]
Amount outstanding	29,900
Current borrowing capacity	$ 70,100
Basis spread on variable rate	3.50%
Promissory note
Debt Instrument [Line Items]
Debt instrument, term	8 years
Interest rate (as a percent)	5.60%
Principal amount	$ 25,000
Unsecured debt payable to U.S. Treasury
Debt Instrument [Line Items]
Total long-term debt, net of debt issue costs	200,600
Line of credit
Debt Instrument [Line Items]
Amount outstanding	0
Maximum borrowing capacity	100,000
Primarily related to acquisition of aircraft and certain spare engines
Debt Instrument [Line Items]
Total long-term debt (including current portion)	3,100,000
Total long-term debt, net of debt issue costs	$ 2,900,000