v3.25.3
Employee benefits - Defined benefit plan expense (Details) - CAD ($)
 12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Disclosure of defined benefit plans [line items]    
Current service cost $ 16,290,000 $ 14,165,000
Past service cost 2,521,000 0
Interest cost 4,221,000 6,101,000
Administration expenses paid from the plan 3,432,000 1,462,000
Defined benefit plan expenses 26,464,000 21,728,000
Costs of services, selling and administrative    
Disclosure of defined benefit plans [line items]    
Defined benefit plan expenses 18,811,000 14,165,000
Net finance costs    
Disclosure of defined benefit plans [line items]    
Defined benefit plan expenses $ 7,653,000 $ 7,563,000