Leases, Commitments and Contingencies - Commitments and Obligations (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Operating lease payments for aircraft and facility obligations
Oct - Dec 2019	$ 17,603
2020	91,892
2021	80,540
2022	70,900
2023	65,521
Thereafter	103,819
Total	430,275
Firm aircraft and spare engine commitments
Oct - Dec 2019	167,037
2020	187,757
2021	11,000
Total	365,794
Interest commitments
Oct - Dec 2019	31,628
2020	116,550
2021	101,468
2022	87,294
2023	71,252
Thereafter	174,805
Total	582,997
Principal maturities on long-term debt
Oct - Dec 2019	91,192
2020	361,131
2021	344,937
2022	358,586
2023	367,322
Thereafter	1,485,420
Total long-term debt	3,008,588	$ 3,185,438
Total commitments and obligations
Oct - Dec 2019	307,460
2020	757,330
2021	537,945
2022	516,780
2023	504,095
Thereafter	1,764,044
Total	$ 4,387,654
Variable interest rate (as a percent)	0.10%
Previously reported
Operating lease payments for aircraft and facility obligations
Oct - Dec 2019	$ 87,256
2020	101,741
2021	90,787
2022	72,593
2023	65,749
Thereafter	59,820
Total	$ 477,946