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Asset retirement obligations - Summary of Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance $ 94,143 $ 99,684
Accretion during the year 2,532 2,038
Revisions to estimate 6,271 (2,043)
Settlements (2,807) (5,536)
Reclassified to liabilities associated with assets held for sale (4,122)  
Ending Balance 96,017 94,143
Less: Current portion (1,782) (824)
Long term portion 94,235 93,319
Estimated undiscounted amount 126,232 135,173
Turkey    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 36,479 37,321
Accretion during the year 981 896
Revisions to estimate 2,330 (1,117)
Settlements (594) (621)
Reclassified to liabilities associated with assets held for sale 0  
Ending Balance 39,196 36,479
Less: Current portion 0 0
Long term portion 39,196 36,479
Estimated undiscounted amount 48,064 48,454
Canada    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 12,215 9,453
Accretion during the year 316 0
Revisions to estimate 107 2,762
Settlements 0 0
Reclassified to liabilities associated with assets held for sale 0  
Ending Balance 12,638 12,215
Less: Current portion 0 0
Long term portion 12,638 12,215
Estimated undiscounted amount 14,998 14,989
Greece    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 40,069 47,461
Accretion during the year 1,090 1,035
Revisions to estimate 3,704 (3,512)
Settlements (2,213) (4,915)
Reclassified to liabilities associated with assets held for sale 0  
Ending Balance 42,650 40,069
Less: Current portion (1,782) (824)
Long term portion 40,868 39,245
Estimated undiscounted amount 56,467 65,274
Romania    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 1,364 1,405
Accretion during the year 39 36
Revisions to estimate 130 (77)
Settlements 0 0
Reclassified to liabilities associated with assets held for sale 0  
Ending Balance 1,533 1,364
Less: Current portion 0 0
Long term portion 1,533 1,364
Estimated undiscounted amount 2,287 2,335
Brazil    
Disclosure of Asset Retirement Obligations [line items]    
Beginning Balance 4,016 4,044
Accretion during the year 106 71
Revisions to estimate 0 (99)
Settlements 0 0
Reclassified to liabilities associated with assets held for sale (4,122)  
Ending Balance 0 4,016
Less: Current portion 0 0
Long term portion 0 4,016
Estimated undiscounted amount $ 4,416 $ 4,121