LONG-TERM DEBT - LINE OF CREDIT (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) credit_facility	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Credit Facilities | credit_facility	3
Line of Credit Facility, Maximum Borrowing Capacity	$ 475,000,000
Line of Credit Facility, Asset Restrictions	500,000,000
Credit Facility 1 [Member] | Secured by aircraft [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 250,000,000		$ 100,000,000
Line of Credit Facility, Expiration Date	Jun. 30, 2021
Credit Facility 2 [Member] | Secured by aircraft [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 75,000,000	$ 52,000,000
Line of Credit Facility, Expiration Date	Sep. 30, 2018
Credit Facility 3 [Member] | Secured by certain accounts receivable, spare engines, spare parts and ground service equipment [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 150,000,000			$ 100,000,000
Line of Credit Facility, Expiration Date	Mar. 31, 2022
Credit Facilities 1 and 2 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Credit Facilities | credit_facility	2