Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Air traffic liability	$ 315,408				$ 291,981				$ 315,408	$ 291,981
Total operating revenues	$ 969,816	$ 991,968	$ 1,012,956	$ 855,796	$ 862,795	$ 904,330	$ 851,771	$ 704,138	3,830,536	3,323,034	$ 2,643,552
Fare
Disaggregation of Revenue [Line Items]
Total operating revenues									1,886,855	1,704,107	1,363,395
Non Fare
Disaggregation of Revenue [Line Items]
Total operating revenues									1,870,750	1,555,908	1,209,492
Passenger
Disaggregation of Revenue [Line Items]
Total operating revenues									3,757,605	3,260,015	2,572,887
Other
Disaggregation of Revenue [Line Items]
Total operating revenues									$ 72,931	$ 63,019	$ 70,665