Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Federal excise and other passenger taxes and fees payable	$ 48,557	$ 42,628
Salaries and wages	34,549	34,209
Airport expenses	27,086	21,726
Federal and state income tax payable	24,944	3,286
Aircraft and facility lease obligations	20,485	10,089
Aircraft maintenance	17,604	16,127
Fuel	12,006	9,508
Other	22,648	15,348
Other current liabilities	$ 207,879	$ 152,921