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Intangible assets, net - Schedule of Amortization Expense Recognized (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]      
Amortization expense $ 2,101 $ 2,063 $ 2,122
Cost of Revenues [Member]      
Finite-Lived Intangible Assets [Line Items]      
Amortization expense 241 243 147
General and administrative expenses [Member]      
Finite-Lived Intangible Assets [Line Items]      
Amortization expense 415 323 386
Research and development expenses [Member]      
Finite-Lived Intangible Assets [Line Items]      
Amortization expense $ 1,445 $ 1,497 $ 1,589