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Other current and non-current non-financial assets (Details 1) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of other non-financials asset [Abstract]      
Opening balance $ 26,189 $ 17,721 $ 23,008
Change in assets for exploration and evaluation of mineral resources      
Additions 0 11,298 0
Short-term reclassifications (1,311) 1,987 595
Increase (decrease) due to transfers and other charges (6,224) (4,817) (5,882)
Total changes (7,535) 8,468 (5,287)
Final balance $ 18,654 $ 26,189 $ 17,721