Leases and Prepaid Maintenance Deposits - Future Minimum Lease Payments Under Noncancelable Operating Leases (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Future Minimum Lease Payments, Operating Leases
2015	$ 243,984
2016	237,751
2017	221,623
2018	198,082
2019	167,817
2020 and thereafter	663,987
Total minimum lease payments	1,733,244
Future Minimum Lease Payments, Capital Leases
2015	1,444
2016	1,044
2017	44
2018	44
2019	12
2020 and thereafter	0
Total minimum lease payments	2,588
Less amount representing interest	205
Present value of minimum lease payments	2,383	2,049
Less current portion	1,289
Long-term portion	1,094
Aircraft and Spare Engine Leases
Future Minimum Lease Payments, Operating Leases
2015	214,337
2016	212,512
2017	196,010
2018	172,323
2019	144,211
2020 and thereafter	592,409
Total minimum lease payments	1,531,802
Property Facility Leases
Future Minimum Lease Payments, Operating Leases
2015	29,647
2016	25,239
2017	25,613
2018	25,759
2019	23,606
2020 and thereafter	71,578
Total minimum lease payments	$ 201,442