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Share-based payments - Stock options (Details) - $ / shares | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022
Disclosure of classes of share capital [line items] |  |
Weighted average share price for share options at date of exercise (in CAD per share) | $ 123.25 | $ 107.09
Stock options |  |
Disclosure of classes of share capital [line items] |  |
Vesting period for stock options | 4 years |
Expiration period for stock options | 10 years |
Stock options | Class A subordinate voting shares |  |
Disclosure of classes of share capital [line items] |  |
Number of shares reserved for issuance under the stock option plan (in shares) | 15,353,015 |

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