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Breakdown of Revenue and Non-Current Assets by Geographical Areas - Narrative (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
market
Mar. 31, 2017
USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]    
Number of geographical markets | market 3  
Revenue from contract with customer $ 564,164 $ 516,667
Sales Revenue, Net    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Concentration risk, percentage 2.20% 1.90%
France    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenue from contract with customer $ 41,500 $ 37,500