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Provisions (Details) - CAD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Provisions [Line Items]    
Beginning of year $ 908,782,000  
Changes in estimates and discont rates [Abstract]    
Capitalized in property, plant and equipment 17,541,000  
Recognized in earnings (503,000)  
Provisions used during the period (14,332,000)  
Unwinding of discount 22,020,000  
Effect of movements in exchange rates (19,968,000)  
End of period 913,540,000  
Current 38,507,000 $ 19,619,000
Non-current 875,033,000 889,163,000
Outstanding letters of credit facility 1,474,155,000 1,470,435,000
Reclamation [Member]    
Provisions [Line Items]    
Beginning of year 899,261,000  
Changes in estimates and discont rates [Abstract]    
Capitalized in property, plant and equipment 17,541,000  
Recognized in earnings 43,000  
Provisions used during the period (13,343,000)  
Unwinding of discount 21,866,000  
Effect of movements in exchange rates (19,968,000)  
End of period 905,400,000  
Current 36,617,000  
Non-current 868,783,000  
Estimated total future decommissioning and reclamation costs $ 1,051,746,000 1,037,302,000
Description of period, majority of expenditures will occur 2022  
Outstanding letters of credit facility $ 1,011,613,000 988,207,000
Reclamation [Member] | Uranium [Member]    
Provisions [Line Items]    
Beginning of year 645,219,000  
Changes in estimates and discont rates [Abstract]    
End of period 669,835,000  
Reclamation [Member] | Fuel Services [Member]    
Provisions [Line Items]    
Beginning of year 254,042,000  
Changes in estimates and discont rates [Abstract]    
End of period 235,565,000  
Waste Disposal [Member]    
Provisions [Line Items]    
Beginning of year 9,521,000  
Changes in estimates and discont rates [Abstract]    
Capitalized in property, plant and equipment 0  
Recognized in earnings (546,000)  
Provisions used during the period (989,000)  
Unwinding of discount 154,000  
Effect of movements in exchange rates 0  
End of period 8,140,000  
Current 1,890,000  
Non-current 6,250,000  
Estimated total future decommissioning and reclamation costs $ 8,239,000 $ 14,930,000