Leases, Commitments and Contingencies - Commitments and Obligations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Operating lease payments for aircraft and facility obligations
Jul - Dec 2019	$ 36,756
2020	93,752
2021	76,687
2022	67,728
2023	62,558
Thereafter	88,144
Total	425,625
Firm aircraft and spare engine commitments
Jul - Dec 2019	79,428
2020	136,598
2021	97,440
Total	313,466
Interest commitments
Jul - Dec 2019	63,949
2020	116,723
2021	101,295
2022	87,294
2023	71,252
Thereafter	174,805
Total	615,318
Principal maturities on long-term debt
Jul - Dec 2019	171,243
2020	361,481
2021	344,587
2022	358,586
2023	367,322
Thereafter	1,485,420
Total long-term debt	3,088,639	$ 3,185,438
Total commitments and obligations
Jul - Dec 2019	351,376
2020	708,554
2021	620,009
2022	513,608
2023	501,132
Thereafter	1,748,369
Total	$ 4,443,048
Variable interest rate (as a percent)	0.10%
Previously reported
Operating lease payments for aircraft and facility obligations
Jul - Dec 2019	$ 87,256
2020	101,741
2021	90,787
2022	72,593
2023	65,749
Thereafter	59,820
Total	$ 477,946