Commitments and Contingencies - Commitments and Obligations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Operating lease payments for aircraft and facility obligations
Total	$ 558,171
July - 2018	43,683
2019	85,317
2020	101,529
2021	93,117
2022	75,178
Therafter	159,347
Firm aircraft and spare engine commitments
Total	626,980
July - 2018	508,740
2019	21,200
2020	10,600
2021	86,440
Interest commitments
Total	600,413
July - 2018	60,497
2019	111,075
2020	96,051
2021	82,139
2022	69,227
Therafter	181,424
Principal maturities on long-term debt
Total	2,994,776	$ 2,712,350
July - 2018	172,320
2019	357,548
2020	330,229
2021	319,827
2022	310,891
Thereafter	1,503,961
Total commitments and obligations
Total	4,780,340
July - 2018	785,240
2019	575,140
2020	538,409
2021	581,523
2022	455,296
Therafter	$ 1,844,732
Variable interest rate (as percent)	1.60%