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Intangible Exploration and Evaluation Assets (Tables)
 12 Months Ended
Dec. 31, 2018
Disclosure of detailed information about intangible assets [abstract]  
Schedule of intangible exploration and evaluation assets
($000s)
 
2018

 
2017

Balance, beginning of year
 
$
41,478

 
$
105,869

Additions
 
9,288

 
16,905

Transfer to petroleum and natural gas assets
 
—

 
(2,271
)
Impairment loss
 
(14,500
)
 
(79,025
)
Balance, end of year
 
$
36,266

 
$
41,478