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Segment Information and Geographic Data - Additional Information (Detail) - Segment
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Segment Reporting Information [Line Items]        
Number of operating segment     1  
Revenue [Member] | Outside Of United States [Member] | Geographic Concentration Risk [Member]        
Segment Reporting Information [Line Items]        
Concentration risk, percentage 33.00% 27.00% 32.00% 27.00%