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Trade and Other Payables - Additional Information (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Trade And Other Payables [Line Items]    
Liabilities arising from contracts with customers $ 756  
Refund Liabilities [Member]    
Trade And Other Payables [Line Items]    
Liabilities arising from contracts with customers $ 3,831 $ 3,929