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REVENUES (Contract Balances) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Change in Contract with Customer, Asset and Liability [Abstract]      
Revenues from performance obligations satisfied in previous period $ 1,704 $ 5,404  
Change in Contract with Customer, Liability [Abstract]      
Revenue recognized 3,051    
Unbilled revenues 17,827   $ 13,522
Accrued expenses and other current liabilities      
Change in Contract with Customer, Liability [Abstract]      
Deferred revenues 8,696   4,558
Other noncurrent liabilities      
Change in Contract with Customer, Liability [Abstract]      
Deferred revenues $ 146   $ 224