LONG-TERM DEBT - LINE OF CREDIT (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) aircraft credit_facility
Line of Credit Facility [Line Items]
Number of credit facilities | credit_facility	3
Number of credit facilities, no borrowing | credit_facility	2
Credit Facilities 1 and 2 [Member]
Line of Credit Facility [Line Items]
Number of credit facilities | credit_facility	2
Credit Facility 1 [Member]
Line of Credit Facility [Line Items]
Line of credit facility, asset restrictions, unrestricted cash and marketable securities | $	$ 500,000,000
Credit Facility 1 [Member] | Secured by aircraft [Member]
Line of Credit Facility [Line Items]
Line of credit facility, borrowing capacity | $	$ 100,000,000
Number of credit facilities | credit_facility	1
Credit Facility 2 [Member] | Secured by other [Member]
Line of Credit Facility [Line Items]
Line of credit facility, borrowing capacity | $	$ 100,000,000
Credit Facility 3 [Member]
Line of Credit Facility [Line Items]
Line of credit facility, borrowing capacity | $	$ 52,000,000
Number of aircrafts used as collateral | aircraft	2
Credit Facility 3 [Member] | Secured by aircraft [Member]
Line of Credit Facility [Line Items]
Number of credit facilities | credit_facility	1
Secured Debt [Member] | Credit Facility 2 [Member]
Line of Credit Facility [Line Items]
Line of credit facility, borrowing capacity | $	$ 100,000,000