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Revenue Recognition (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Performance Obligation, Description of Timing The expected duration of the performance obligation is less than one year.  
Impairment losses on receivables $ 0  
Maximum [Member]    
Contracts and contract liabilities duration period 1 year  
Opening [Member]    
Contract liability $ 219 $ 235