INVENTORY AND LONG-TERM PARTS INVENTORY (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Lower of cost or net realizable value inventory adjustments	$ 348	$ 1,462	$ 0	$ 0	$ 930	$ 0	$ 76	$ 705	$ 1,810	$ 1,711	$ 6,379