Leases and Prepaid Maintenance Deposits - Future Minimum Lease Payments Under Noncancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Total Operating and Capital Lease Obligations
2019	$ 229,693
2020	200,476
2021	185,606
2022	170,011
2023	147,847
2024 and thereafter	439,802
Total minimum lease payments	1,373,435
Office Equipment
Capital Leases
2019	810
2020	408
2021	186
2022	158
2023	145
2024 and thereafter	0
Total minimum lease payments	1,707
Less amount representing interest	152
Present value of minimum lease payments	1,555
Less current portion	721
Long-term portion	834
Aircraft and Spare Engine Leases
Operating Leases
2019	176,256
2020	170,106
2021	168,416
2022	155,135
2023	133,915
2024 and thereafter	350,266
Total minimum lease payments	1,154,094
Property Facility Leases
Operating Leases
2019	52,627
2020	29,962
2021	17,004
2022	14,718
2023	13,787
2024 and thereafter	89,536
Total minimum lease payments	$ 217,634

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