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Employee benefits - Sensitivity analysis for actuarial assumptions (Details) - CAD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Actuarial assumption of discount rates | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ (15,631) $ (19,249)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 16,416 $ 20,234
Actuarial assumption of discount rates | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ (2,370) $ (2,294)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 2,473 $ 2,500
Actuarial assumption of discount rates | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ (1,596) $ (1,512)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 1,663 $ 1,578
Actuarial assumption of expected rates of salary increases | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 137 $ 193
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (132) $ (188)
Actuarial assumption of expected rates of salary increases | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 2,572 $ 2,584
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (2,474) $ (2,388)
Actuarial assumption of expected rates of salary increases | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 23 $ 20
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (21) $ (19)
Actuarial assumption of expected rates of pension increases | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 8,713 $ 13,324
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (8,503) $ (12,614)
Actuarial assumption of expected rates of pension increases | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 0 $ 0
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 0 $ 0
Actuarial assumption of expected rates of pension increases | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 834 $ 774
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (805) $ (747)
Actuarial assumption of expected rates of inflation | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 12,348 $ 21,301
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (11,948) $ (16,005)
Actuarial assumption of expected rates of inflation | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 5,660 $ 2,584
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (5,110) $ (2,388)
Actuarial assumption of expected rates of inflation | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 834 $ 774
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (805) $ (747)
Actuarial assumption of life expectancy after retirement | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Period of reasonably possible increase in actuarial assumption 1 year 1 year
Period of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 12,614 $ 12,957
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (12,801) $ (13,093)
Actuarial assumption of life expectancy after retirement | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Period of reasonably possible increase in actuarial assumption 1 year 1 year
Period of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 943 $ 281
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (1,258) $ (320)
Actuarial assumption of life expectancy after retirement | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Period of reasonably possible increase in actuarial assumption 1 year 1 year
Period of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 1,702 $ 1,511
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (1,530) $ (1,360)