Revenue Recognition - Frequent Flyer Liability (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Air traffic liability and current frequent flyer deferred revenue	$ 553,554	$ 606,684
Noncurrent frequent flyer deferred revenue	179,740	175,218
Frequent Flyer Revenue
Disaggregation of Revenue [Line Items]
Air traffic liability and current frequent flyer deferred revenue	195,500	174,588
Noncurrent frequent flyer deferred revenue	179,740	175,218
Total frequent flyer liability	$ 375,240	$ 349,806