Revenue Recognition - Frequent Flyer Liability (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Air traffic liability and current frequent flyer deferred revenue	$ 623,741	$ 606,684
Noncurrent frequent flyer deferred revenue	172,281	175,218
Frequent Flyer Revenue
Disaggregation of Revenue [Line Items]
Air traffic liability and current frequent flyer deferred revenue	187,387	174,588
Noncurrent frequent flyer deferred revenue	172,281	175,218
Total frequent flyer liability	$ 359,668	$ 349,806