Long-term Debt (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Current portion of long-term debt	$ 489,468	$ 539,061
Less current portion of unamortized debt issue cost, net	(3,349)	(3,472)
Current portion of long-term debt, net of debt issue costs	486,119	535,589
Long-term debt, net of current maturities	2,089,119	2,153,558
Less long-term portion of unamortized debt issue cost, net	(15,656)	(16,772)
Long-term debt, net of current maturities and debt issue costs	2,073,463	2,136,786
Total long-term debt (including current portion)	2,578,587	2,692,619
Total unamortized debt issue cost, net	(19,005)	(20,244)
Total long-term debt, net of debt issue costs	2,559,582	2,672,375
Maximum borrowing capacity	$ 100,000
Effective interest rate (as a percent)	4.30%
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	$ 47,100	$ 47,100
Letters of credit
Debt Instrument [Line Items]
Amount outstanding	$ 25,000
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	75,000
Primarily related to acquisition of aircraft and certain spare engines
Debt Instrument [Line Items]
Total long-term debt (including current portion)	2,600,000
Total long-term debt, net of debt issue costs	$ 2,400,000