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Related Party Balances - Additional Information (Detail) - DTDW - NIGERIA - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Related Party Transaction [Line Items]    
Due from related party $ 44,233 $ 33,353
Due to related party $ 15,611 9,645
Trade and Other Receivables, Net    
Related Party Transaction [Line Items]    
Due from related party   33,400
Accounts Payable    
Related Party Transaction [Line Items]    
Due to related party   $ 9,600