Long-term Debt (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) aircraft	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Current portion long-term debt	$ 368,558	$ 367,954
Less current portion of unamortized debt issue cost, net	(3,979)	(3,828)
Current portion of long-term debt, net of debt issue costs	364,579	364,126
Long-term debt, net of current maturities	2,558,704	2,649,569
Less long-term portion of unamortized debt issue cost, net	(21,091)	(20,580)
Long-term debt, net of current maturities and debt issue costs	2,537,613	2,628,989
Total long-term debt (including current portion)	2,927,262	3,017,523
Total unamortized debt issue cost, net	(25,070)	(24,408)
Total	2,902,192	2,993,115
Debt issued	$ 0
Number of aircraft leased | aircraft	103
Maximum borrowing capacity	$ 75,000
Amount outstanding	0
Current borrowing capacity	66,200
Letters of credit and surety bonds
Debt Instrument [Line Items]
Amount outstanding	61,800	$ 61,700
Letters of credit
Debt Instrument [Line Items]
Amount outstanding	$ 8,800