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Accounts Receivable - Maturity of Portfolio of Accounts Receivable (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Disclosure of accounts receivables [line items]    
Trade and other receivables $ 121,758 $ 119,839
Financial assets neither past due nor impaired [member]    
Disclosure of accounts receivables [line items]    
Trade and other receivables 115,685 110,524
Financial assets not impaired [member]    
Disclosure of accounts receivables [line items]    
Trade and other receivables 118,085 116,100
Financial assets not impaired [member] | Past due 1 to 30 days [member]    
Disclosure of accounts receivables [line items]    
Trade and other receivables 1,286 711
Financial assets not impaired [member] | Past due 31 to 60 days [member]    
Disclosure of accounts receivables [line items]    
Trade and other receivables 617 914
Financial assets not impaired [member] | More than 60 days [member]    
Disclosure of accounts receivables [line items]    
Trade and other receivables 497 3,951
Impaired [member]    
Disclosure of accounts receivables [line items]    
Trade and other receivables $ 3,673 $ 3,739