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Property, plant and equipment - Additional information (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about property, plant and equipment [line items]        
Capitalized interest     $ 0 $ 3,848,000
Increase (decrease) in proven and probable reserves (as a percent) (23.00%)      
Write-down of assets     38,660,000 6,298,000
Cost        
Disclosure of detailed information about property, plant and equipment [line items]        
Write-down of assets     $ 40,030,000 1,995,000
Reversal (impairment) of property, plant and equipment       $ (3,578,000)
Individual assets or cash-generating units | Turkey        
Disclosure of detailed information about property, plant and equipment [line items]        
Reversal (impairment) of property, plant and equipment   $ 100,492,000    
Reversal (impairment) of property, plant and equipment, net of deferred tax   80,143,000    
Impairment loss recognised in profit or loss, property, plant and equipment   15,269,000    
Impairment loss recognised in profit or loss, property, plant and equipment, net of deferred tax   $ 11,910,000