XML 166 R140.htm IDEA: XBRL DOCUMENT v3.20.4
Intangible assets and goodwill (Details 1) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Intangible assets other than goodwill $ 178,407 $ 188,358 $ 189,350
Goodwill 41,966 34,726 34,866
Total intangible assets and goodwill $ 220,373 $ 223,084 224,216
Computer software [member] | Finite intangible assets [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Finite Finite  
Intangible assets other than goodwill $ 4,826 $ 6,011  
Total intangible assets and goodwill 4,826 6,011 4,568
Goodwill [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Goodwill $ 41,966 $ 34,726  
Goodwill [Member] | Indeifinite Intangible assets [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Indefinite Indefinite  
Mining rights [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Unit-production method    
Mining rights [Member] | Finite intangible assets [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Finite Finite  
Intangible assets other than goodwill $ 150,046 $ 157,570  
Total intangible assets and goodwill $ 150,046 $ 157,570 159,256
Water rights and rights of way [member] | Indeifinite Intangible assets [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Indefinite Indefinite  
Intangible assets other than goodwill $ 23,343 $ 23,342  
Total intangible assets and goodwill $ 23,343 $ 23,342 23,776
Customer-related intangible assets [member] | Finite intangible assets [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Finite Finite  
Intangible assets other than goodwill $ 0 $ 1,273  
Total intangible assets and goodwill $ 0 $ 1,273 1,573
Other Intangible Assets [Member] | Finite intangible assets [Member]      
Disclosure Of Intangible Assets And Goodwill [Line Items]      
Useful life Finite Finite  
Intangible assets other than goodwill $ 192 $ 162  
Total intangible assets and goodwill $ 192 $ 162 $ 177