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Revenues - Narrative (Details)
3 Months Ended
Mar. 31, 2018
country
customer
Mar. 31, 2017
Revenue from Contract with Customer [Abstract]    
Number of customers | customer 500  
Number of countries in which customers are located | country 40  
Minimum [Member]    
Concentration Risk [Line Items]    
Length of contracts 1 year  
Maximum [Member]    
Concentration Risk [Line Items]    
Length of contracts 2 years  
10 Largest Customers [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]    
Concentration Risk [Line Items]    
Concentration risk percentage 47.00% 43.00%