Commitments and Contingencies - Future Minimum Lease Payments Under Capital Leases and Noncancelable Operating Leases (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Operating Leased Assets [Line Items]
Lease term	3 years
Total Operating and Capital Lease Obligations
remainder of 2017	$ 65,560
2018	248,555
2019	226,122
2020	206,634
2021	183,411
2022 and thereafter	643,262
Total minimum lease payments	1,573,544
Fixed Maintenance Reserve Payments, Aircraft and Related Flight Equipment [Member]
Committed Expenditures
Committed expenditures, remainder of 2017	1,900
Committed expenditures, 2018	6,900
Committed expenditures, 2019	5,700
Committed expenditures, 2020	5,400
Committed expenditures, 2021	5,500
Committed expenditures, 2022 and beyond	17,700
Non-aircraft Related Commitments [Member]
Committed Expenditures
Committed expenditures, remainder of 2017	1,800
Committed expenditures, 2018	5,700
Committed expenditures, 2019	1,600
Committed expenditures, 2020	1,000
Committed expenditures, 2021	500
Committed expenditures, 2022 and beyond	200
Capital Lease Obligations [Member]
Capital Leases
remainder of 2017	134
2018	537
2019	504
2020	188
2021	28
2022 and thereafter	0
Total minimum lease payments	1,391
Less amount representing interest	114
Present value of minimum lease payments	1,277
Less current portion	468
Long-term portion	809
Aircraft and Spare Engine Leases [Member]
Operating Leases
remainder of 2017	53,017
2018	204,292
2019	189,106
2020	180,842
2021	170,643
2022 and thereafter	570,120
Total minimum lease payments	1,368,020
Property Facility Leases [Member]
Operating Leases
remainder of 2017	12,409
2018	43,726
2019	36,512
2020	25,604
2021	12,740
2022 and thereafter	73,142
Total minimum lease payments	$ 204,133