Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Salaries, wages and benefits	$ 92,983	$ 89,163
Airport obligations	57,767	80,134
Aircraft and facility lease obligations	50,529	20,656
Federal excise and other passenger taxes and fees payable	33,851	65,312
Aircraft maintenance	24,434	38,099
Interest payable	23,276	16,941
Fuel	8,694	28,510
Other	35,116	34,706
Other current liabilities	$ 326,650	$ 373,521