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Significant Accounting Policies - Summary of Company's Ownership Percentage in Each of Its Subsidiaries (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
NXE Energy Royalty Ltd [member]    
Disclosure of subsidiaries [line items]    
Proportion of ownership interest in subsidiary 100.00%  
NXE Energy SW1 Ltd [member]    
Disclosure of subsidiaries [line items]    
Proportion of ownership interest in subsidiary 100.00%  
NXE Energy SW3 Ltd [member]    
Disclosure of subsidiaries [line items]    
Proportion of ownership interest in subsidiary 100.00%  
IsoEnergy Ltd. [member]    
Disclosure of subsidiaries [line items]    
Proportion of ownership interest in subsidiary 53.35% 63.90%