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Segment and Geographic Information (Details) - segment
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Number of reportable segments     1  
Concentration risk percentage 102.00% 102.00% 103.00% 104.00%
UNITED STATES        
Percent of consolidated long-lived assets     100.00%  
Revenue        
Concentration risk percentage 100.00% 100.00% 100.00% 100.00%
Revenue | UNITED STATES        
Concentration risk percentage     99.00% 99.00%