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Geographic Information and Concentrations of Risk - Schedule of Geographic Concentration of Net Revenues (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]    
Net revenues $ 46,733 $ 55,389
United States and Canada    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Net revenues 30,106 39,355
South Africa    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Net revenues 10,685 9,822
Other    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Net revenues $ 5,942 $ 6,212