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DEFERRED REVENUE (Narrative) (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Deferred revenue $ 8,476   $ 8,658
Revenue $ 121,794 $ 133,882  
Minimum [Member]      
Expected to be recognized over periods performance obligations 11 years    
Maximum [Member]      
Expected to be recognized over periods performance obligations 15 years    
Recognized over time for service [Member]      
Revenue     $ 3,307