Revenue Recognition - Frequent Flyer Liability (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Air traffic liability and current frequent flyer deferred revenue	$ 515,424	$ 606,684
Noncurrent frequent flyer deferred revenue	186,618	175,218
Frequent flyer revenue
Disaggregation of Revenue [Line Items]
Air traffic liability and current frequent flyer deferred revenue	202,981	174,588
Noncurrent frequent flyer deferred revenue	186,618	175,218
Total frequent flyer liability	$ 389,599	$ 349,806