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Capital stock - Narrative (Details) |  |  |  | 12 Months Ended
--- | --- | --- | --- | ---
Nov. 05, 2025 $ / shares | Jan. 28, 2025 shares | Feb. 23, 2024 CAD ($) shares | Sep. 30, 2025 CAD ($) shares vote | Sep. 30, 2024 CAD ($) shares
Disclosure of classes of share capital [line items] |  |  |  |  |
Withholding taxes remitted on the net settlement of performance share units |  |  |  | $ 52,888,000 | $ 15,407,000
Purchase of treasury shares |  |  |  | 13,323,000 | 66,847,000
Exercise of stock options |  |  |  | 61,989,000 | 76,535,000
Purchase and cancellation of Class A subordinate voting shares |  |  |  | 1,274,530,000 | 934,765,000
Net tax liability related to shares repurchased and issued |  |  |  | 22,218,000 | 13,565,000
Tax payment related to shares repurchased and issued |  |  |  | $ 25,999,000 | $ 0
Major ordinary share transactions |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Dividends declared (in CAD per share) | $ / shares | $ 0.17 |  |  |  |
PSUs |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Release of Class A subordinate voting shares held in trusts (in shares) | shares |  |  |  | 765,318 | 280,265
Capital stock |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Release of Class A subordinate voting shares held in trusts (in shares) | shares |  |  |  | 0 | 0
Release of Class A subordinate voting shares held in trusts |  |  |  | $ 46,050,000 | $ 14,078,000
Purchase of treasury shares |  |  |  | 13,323,000 | 66,847,000
Exercise of stock options |  |  |  | $ 74,319,000 | $ 91,800,000
Purchased and cancelled (in shares) | shares |  |  |  | 8,781,243,000 | 6,597,158,000
Purchased and cancelled |  |  |  | $ 77,462,000 | $ 45,878,000
Capital stock | PSUs |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Release of Class A subordinate voting shares held in trusts (in shares) | shares |  |  |  | 438,458 | 171,751
Contributed surplus |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Exercise of stock options |  |  |  | $ (12,330,000) | $ (15,265,000)
Preferred shares | Capital stock |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Number of votes per share | vote |  |  |  | 1 |
Class A subordinate voting shares | Capital stock |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Number of votes per share | vote |  |  |  | 1 |
Release of Class A subordinate voting shares held in trusts (in shares) | shares |  |  |  | 0 | 0
Release of Class A subordinate voting shares held in trusts |  |  |  | $ 46,050,000 | $ 14,078,000
Shares purchased (in shares) | shares |  |  |  | 84,456 | 463,364
Purchase of treasury shares |  |  |  | $ 13,323,000 | $ 66,847,000
Exercise of stock options |  |  |  | $ 74,319,000 | $ 91,800,000
Purchased and cancelled (in shares) | shares |  |  |  | 8,781,243,000 | 6,597,158,000
Purchased and cancelled |  |  |  | $ 77,462,000 | $ 45,878,000
Class A subordinate voting shares | Capital stock | Current normal course issuer bid |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Number of shares authorized for purchase and cancellation (in shares) | shares |  | 20,196,413 |  |  |
Purchased and cancelled (in shares) | shares |  |  | 1,674,930 | 80,300 |
Purchased and cancelled |  |  | $ 250,000,000 | $ 708,000 |
Purchase and cancellation of Class A subordinate voting shares |  |  |  | $ 9,935,000 |
Share issue related cost |  |  | 370,000 |  |
Class A subordinate voting shares | Capital stock | Previous and current normal course issuer bid |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled (in shares) | shares |  |  |  | 8,861,543 | 1,965,800
Purchased and cancelled |  |  |  | $ 1,258,466,000 | $ 275,218,000
Class A subordinate voting shares | Capital stock | Normal course issuer bid - Caisse de depot |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled (in shares) | shares |  |  |  |  | 2,887,878
Purchased and cancelled |  |  |  |  | $ 400,000,000
Class A subordinate voting shares | Capital stock | Previous normal course issuer bid |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled (in shares) | shares |  |  |  |  | 68,550
Purchased and cancelled |  |  |  |  | $ 558,000
Purchase and cancellation of Class A subordinate voting shares |  |  |  |  | $ 9,177,000
Class A subordinate voting shares | Capital stock | Co-Founder and Advisor to the Executive Chairman of the Board |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Reclassified between classes of share capital (in shares) | shares |  |  |  |  | (900,000)
Class A subordinate voting shares | Capital stock | Company Wholly-owned by the Founder and Executive Chairman of the Board |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Reclassified between classes of share capital (in shares) | shares |  |  |  |  | (1,422,948)
Class A subordinate voting shares | Capital stock | PSUs |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Shares outstanding, held in trust (in shares) | shares |  |  |  | 2,247,354 | 2,601,356
Class A subordinate voting shares | Contributed surplus |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Exercise of stock options |  |  |  | $ 12,330,000 | $ 15,265,000
Class A subordinate voting shares | Retained earnings | Current normal course issuer bid |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled |  |  | $ 244,821,000 |  |
Class A subordinate voting shares | Retained earnings | Previous and current normal course issuer bid |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled |  |  |  | $ 1,181,004,000 | 258,883,000
Class A subordinate voting shares | Retained earnings | Normal course issuer bid - Caisse de depot |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled |  |  |  |  | $ 375,636,000
Class B shares (multiple voting) | Capital stock |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Number of votes per share | vote |  |  |  | 10 |
Release of Class A subordinate voting shares held in trusts (in shares) | shares |  |  |  | 0 | 0
Release of Class A subordinate voting shares held in trusts |  |  |  | $ 0 | $ 0
Purchase of treasury shares |  |  |  | 0 | 0
Exercise of stock options |  |  |  | $ 0 | $ 0
Purchased and cancelled (in shares) | shares |  |  |  | 0 | 0
Purchased and cancelled |  |  |  | $ 0 | $ 0
Class B shares (multiple voting) | Capital stock | Co-Founder and Advisor to the Executive Chairman of the Board |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Reclassified between classes of share capital (in shares) | shares |  |  |  |  | 900,000
Class B shares (multiple voting) | Capital stock | Company Wholly-owned by the Founder and Executive Chairman of the Board |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Reclassified between classes of share capital (in shares) | shares |  |  |  |  | 1,422,948
Class B multiple voting shares converted to Class A subordinate voting shares | Capital stock | Current normal course issuer bid |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Purchased and cancelled (in shares) | shares |  |  | 1,266,366 |  |

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