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Geographic And Customer Information (Narrative) (Details)
12 Months Ended
Dec. 31, 2017
Rate
Dec. 31, 2016
Rate
Dec. 31, 2015
Rate
Segment Reporting Information [Line Items]      
Concentration risk, percentage 31.00% 30.00% 31.00%
Number of customers accounting for concentration of risk 1 1 1,000