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Segment and Geographic Information - Additional Information (Details) - Segment
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Operating Segments [Abstract]        
Number of operating segments 2      
Number of reportable segments   2    
Revenue | Customer concentration risk | Cisco Systems        
Disclosure of major customers [line items]        
Concentration risk percentage   14.00% 18.00% 19.00%
Revenue | Customer concentration risk | Dell Inc        
Disclosure of major customers [line items]        
Concentration risk percentage   10.00%    
Revenue | Customer concentration risk | Top two customers        
Disclosure of major customers [line items]        
Concentration risk percentage     31.00% 30.00%