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EXPLORATION AND EVALUATION ASSETS (Tables)
 12 Months Ended
Dec. 31, 2017
Exploration For And Evaluation Of Mineral Resources [Abstract]  
Disclosure of detailed information about exploration and evaluation assets
($000s)
 

Cost
 

Balance, December 31, 2015
$
87,919

Additions
2,349

Dispositions
(31,176
)
Transfer to oil and natural gas properties
(29,846
)
Balance, December 31, 2016
29,246

Additions
1,664

Dispositions
(7,843
)
Transfer to oil and natural gas properties
(336
)
Balance, December 31, 2017
$
22,731