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Asset retirement obligations - Summary of asset retirement obligations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance $ 96,017 $ 94,143
Accretion during the year 1,945 2,532
Revisions to estimate 15,769 6,271
Settlements (2,301) (2,807)
Disposal (52)  
Reclassified to liabilities associated with assets held for sale   (4,122)
Ending Balance 111,378 96,017
Less: Current portion (4,701) (1,782)
Long term portion 106,677 94,235
Estimated undiscounted amount 138,687 126,232
Turkey    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 39,196 36,479
Accretion during the year 753 981
Revisions to estimate 5,539 2,330
Settlements (672) (594)
Disposal 0  
Reclassified to liabilities associated with assets held for sale   0
Ending Balance 44,816 39,196
Less: Current portion 0 0
Long term portion 44,816 39,196
Estimated undiscounted amount 56,752 48,064
Canada    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 12,638 12,215
Accretion during the year 243 316
Revisions to estimate 80 107
Settlements 0 0
Disposal 0  
Reclassified to liabilities associated with assets held for sale   0
Ending Balance 12,961 12,638
Less: Current portion 0 0
Long term portion 12,961 12,638
Estimated undiscounted amount 14,218 14,998
Greece    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 42,650 40,069
Accretion during the year 863 1,090
Revisions to estimate 10,056 3,704
Settlements (1,629) (2,213)
Disposal 0  
Reclassified to liabilities associated with assets held for sale   0
Ending Balance 51,940 42,650
Less: Current portion (4,701) (1,782)
Long term portion 47,239 40,868
Estimated undiscounted amount 65,564 56,467
Romania    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 1,533 1,364
Accretion during the year 34 39
Revisions to estimate 94 130
Settlements 0 0
Disposal 0  
Reclassified to liabilities associated with assets held for sale   0
Ending Balance 1,661 1,533
Less: Current portion 0 0
Long term portion 1,661 1,533
Estimated undiscounted amount 2,153 2,287
Brazil    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 0 4,016
Accretion during the year 52 106
Revisions to estimate 0 0
Settlements 0 0
Disposal (52)  
Reclassified to liabilities associated with assets held for sale   (4,122)
Ending Balance 0 0
Less: Current portion 0 0
Long term portion 0 0
Estimated undiscounted amount $ 0 $ 4,416