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Right of Use Assets - Summary of Prepaid Land Lease Payments (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2019
Disclosure Of Quantitative Information About Rightofuse Assets [Abstract]      
Carrying amount, beginning balance $ 1,103    
Recognized lease expense during the year (38) $ (35)  
Exchange difference (53)    
Carrying amount, ending balance 1,012 $ 1,103  
Current portion included in prepayments 34    
Non-current portion included in prepaid land lease payments $ 978   $ 0