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Geographic Information and Concentrations of Risk - Schedule of Geographic Concentration of Assets (Detail) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]    
Assets by Geographic Concentration, Total $ 158,716 $ 198,753
United States and Canada    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Assets by Geographic Concentration, Total 71,564 112,424
South Africa    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Assets by Geographic Concentration, Total 63,693 60,580
Other    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Assets by Geographic Concentration, Total $ 23,459 $ 25,749