Long-term Debt (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Current portion of long-term debt	$ 501,265	$ 447,534
Current portion of unamortized debt issue cost, net	(3,521)	(3,665)
Current portion of long-term debt, net of debt issue costs	497,744	443,869
Long-term debt, net of current maturities	2,302,793	2,582,776
Long-term portion of unamortized debt issue cost, net	(18,418)	(20,593)
Long-term debt, net of current maturities and debt issue costs	2,284,375	2,562,183
Total long-term debt (including current portion)	2,804,058	3,030,310
Total unamortized debt issue cost, net	(21,939)	(24,258)
Total long-term debt, net of debt issue costs	2,782,119	3,006,052
Maximum borrowing capacity	$ 100,000
Effective interest rate (as a percent)	4.10%
Basis spread on variable rate	3.50%
Letters of credit and surety bonds
Debt Instrument [Line Items]
Letters of credit and surety bonds outstanding with various banks and surety institutions	$ 45,000	$ 49,100
Letters of credit
Debt Instrument [Line Items]
Amount outstanding	$ 24,900
Basis spread on variable rate	3.50%
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	75,100
Primarily related to acquisition of aircraft and certain spare engines
Debt Instrument [Line Items]
Total long-term debt (including current portion)	2,800,000
Total long-term debt, net of debt issue costs	$ 2,600,000