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Income taxes - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Major components of tax expense income [line items]    
Tax effect of tax losses $ 160,052 $ 167,030
Tax effect of total losses not recognized as deferred tax assets 160,052 167,030
Deductible temporary differences for which deferred tax assets have not been recognized 11,967 11,253
Temporary differences associated with investments in subsidiaries 546,403 $ 788,137
Turkey [member]    
Major components of tax expense income [line items]    
Increase in deferred income tax expense due to exchange difference $ 24,595