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Property and Equipment, Net - Property and Equipment, Net by Geographic Area (Parenthetical) (Details) - Country
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Geographic Concentrations | Property and Equipment Net | Rest of World    
Revenues From External Customers And Long Lived Assets [Line Items]    
Number of individual country exceeded 10% of total property and equipment 0 0