COMMITMENTS AND CONTINGENCIES - Schedule of Purchase Commitment and Commitment Expenditures (Details) - Subsequent Event $ in Thousands	Feb. 08, 2018 USD ($) aircraft
Related Option Expenditures
Unrecorded Unconditional Purchase Obligation Due in Remainder of Fiscal Year, Deferred Payment | $	$ 63,000
Aircraft
Number of Aircraft Unconditional Commitments
Three Months Ending March 31, 2018	0
2019	1
2020	4
2021	4
2022 and thereafter	18
Purchase Commitment - Total Aircrafts	27
Commitment Expenditures
Three Months Ending March 31, 2018 | $	$ 3,242
2019 | $	19,856
2020 | $	88,506
2021 | $	78,726
2022 and thereafter | $	285,295
Purchase Commitments - Total | $	$ 475,625
Number of Aircraft Conditional Commitments
Three Months Ending March 31, 2018	0
2019	2
2020	2
2021	0
2022 and thereafter	0
Aircraft Purchase Options - Total Aircrafts	4
Related Option Expenditures
Three Months Ending March 31, 2018 | $	$ 0
2019 | $	44,181
2020 | $	31,536
2021 | $	0
2022 and thereafter | $	0
Aircraft Purchase Options - Total | $	$ 75,717
Cancellable Commitments
Number of Aircraft Unconditional Commitments
Purchase Commitment - Total Aircrafts	5
Commitment Expenditures
Purchase Commitments - Total | $	$ 96,000
Related Option Expenditures
Deposit assets | $	4,500
Medium and large | Aircraft
Commitment Expenditures
Three Months Ending March 31, 2018 | $	0
2019 | $	19,856
2020 | $	25,536
2021 | $	78,726
2022 and thereafter | $	285,295
Purchase Commitments - Total | $	$ 409,413
Large | Aircraft
Number of Aircraft Unconditional Commitments
Three Months Ending March 31, 2018	0
2019	1
2020	0
2021	4
2022 and thereafter	18
Purchase Commitment - Total Aircrafts	23
Number of Aircraft Conditional Commitments
Three Months Ending March 31, 2018	0
2019	2
2020	2
2021	0
2022 and thereafter	0
Aircraft Purchase Options - Total Aircrafts	4
U.K. SAR | Aircraft
Number of Aircraft Unconditional Commitments
Three Months Ending March 31, 2018	0
2019	0
2020	4
2021	0
2022 and thereafter	0
Purchase Commitment - Total Aircrafts	4
Commitment Expenditures
Three Months Ending March 31, 2018 | $	$ 3,242
2019 | $	0
2020 | $	62,970
2021 | $	0
2022 and thereafter | $	0
Purchase Commitments - Total | $	$ 66,212