LEASES - Lease cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finance lease cost
Amortization of leased assets	$ 12,536	$ 11,948	$ 13,104
Interest on lease liabilities	8,021	8,659	10,741
Operating lease cost
Short-term	277	1,813	5,345
Total Lease cost	43,396	57,517	80,513
Over-market rent and maintenance reserves
Operating lease cost
Credits for amortization of Over-market Liabilities	7,609	14,110	20,386
Aircraft
Operating lease cost
Included in ROU asset	18,608	30,717	40,043
Variable	(1,232)	(1,541)
Variable			4,520
Other.
Operating lease cost
Included in ROU asset	3,976	4,872	5,415
Variable	$ 1,210	$ 1,049	$ 1,345