Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Federal excise and other passenger taxes and fees payable	$ 62,708	$ 42,064
Salaries and wages	49,109	54,578
Airport obligations	47,230	43,989
Aircraft maintenance	33,092	30,233
Aircraft and facility lease obligations	12,919	10,378
Interest payable	8,953	8,499
Fuel	7,846	14,828
Other	22,772	21,442
Other current liabilities	$ 244,629	$ 226,011