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Disclosure of detailed information about employee future benefit expense (Details) - Other employee benefits [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Statements [Line Items]    
Current service cost $ 3,710 $ 2,614
Net interest expense 3,683 3,567
Components recognized in income statements $ 7,393 $ 6,181