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Intangible Assets - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]      
Discount rates 12.92%    
Decrease in discount rate 11.50%    
Increase in discount rate 13.50%    
Impairment loss   $ 5,900  
Intangible assets $ 81,115 69,502 $ 69,426
Goodwill [member]      
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]      
Estimated recoverable amount 4,400,000 3,500,000  
Carrying amount $ 20,400    
Percentage of growth rate 3.10%    
Estimated recoverable amount of CGU exceed its carrying value by 92.00%    
Intangible assets $ 20,380 20,380 $ 20,380
Capitalised development expenditure [member]      
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]      
Intangible assets   $ 11,800