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Asset retirement obligations (Tables)
 12 Months Ended
Dec. 31, 2018
Disclosure of asset retirement obligations [abstract]  
Summary of Asset Retirement Obligations
 
Turkey

Canada

Greece

Romania

Brazil

Total

 
 
 
 
 
 
 
At January 1, 2018
$
37,321

$
9,453

$
47,461

$
1,405

$
4,044

$
99,684

Accretion during the year
896

—

1,035

36

71

2,038

Revisions to estimate
(1,117
)
2,762

(3,512
)
(77
)
(99
)
(2,043
)
Settlements
(621
)
—

(4,915
)
—

—

(5,536
)
At December 31, 2018
36,479

12,215

40,069

1,364

4,016

94,143

Less: Current portion
—

—

(824
)
—

—

(824
)
Long term portion
36,479

12,215

39,245

1,364

4,016

93,319

Estimated undiscounted amount
$
48,454

$
14,989

$
65,274

$
2,335

$
4,121

$
135,173


 
Turkey

Canada

Greece

Romania

Brazil

Total

 
 
 
 
 
 
 
At January 1, 2017
$
36,196

$
—

$
48,131

$
1,359

$
4,092

$
89,778

Acquired during the year
—

9,453

—

—

—

9,453

Accretion during the year
913

—

1,025

36

32

2,006

Revisions to estimate
502

—

1,112

10

(80
)
1,544

Settlements
(290
)
—

(2,807
)
—

—

(3,097
)
At December 31, 2017
37,321

9,453

47,461

1,405

4,044

99,684

Less: Current portion
—

—

(3,489
)
—

—

(3,489
)
Long term portion
37,321

9,453

43,972

1,405

4,044

96,195

Estimated undiscounted amount
$
49,257

$
12,286

$
71,591

$
2,340

$
4,117

$
139,591
Summary of Present Value of Estimated Future Net Cash Outflows
The provision is calculated as the present value of estimated future net cash outflows based on the following key assumptions:
 
Turkey
Canada
Greece
Romania
Brazil

 
%
%
%
%
%

At December 31, 2017
 
 
 
 
 
Inflation rate
 2.0 to 2.2
 2.0 to 2.2
 2.0 to 2.2
 2.0 to 2.2
 2.0 to 2.2

Discount rate
 2.3 to 2.5
 2.3 to 2.5
 1.5 to 3.0
2.7
1.8

 
 
 
 
 
 
At December 31, 2018
 
 
 
 
 
Inflation rate
 2.2 to 2.3
 2.2 to 2.3
 2.2 to 2.3
 2.2 to 2.3
 2.2 to 2.3

Discount rate
2.7
2.7
 2.5 to 2.9
2.9
2.6