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Investments in subsidiaries - Narrative (Details) | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 CAD ($) | Aug. 28, 2025 CAD ($) employee | Mar. 24, 2025 employee | Mar. 20, 2025 employee | Feb. 24, 2025 CAD ($) employee | Dec. 13, 2024 CAD ($) employee | Sep. 30, 2024 CAD ($)
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Net assets acquired | $ 1,931,252,000 |  |  |  |  |  | $ 390,249,000
Additional recognition, acquisition costs | 11,510,000 |  |  |  |  |  |
Daugherty |  |  |  |  |  |  |
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Net assets acquired | 343,024,000 |  |  |  |  | $ 343,024,000 |
Number of professionals employed | employee |  |  |  |  |  | 1,100 |
Revenue of acquiree since acquisition date | 220,000,000 |  |  |  |  |  |
Profit (loss) of acquiree since acquisition date | 22,000,000 |  |  |  |  |  |
Revenue of combined entity as if combination occurred at beginning of period | 1,120,000,000 |  |  |  |  |  |
Profit (loss) of combined entity as if combination occurred at beginning of period | 46,000,000 |  |  |  |  |  |
BJSS |  |  |  |  |  |  |
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Net assets acquired | 1,255,577,000 |  |  |  | $ 1,255,577,000 |  |
Number of professionals employed | employee |  |  |  |  | 2,400 |  |
Revenue of acquiree since acquisition date | 299,000,000 |  |  |  |  |  |
Profit (loss) of acquiree since acquisition date | 24,000,000 |  |  |  |  |  |
Revenue of combined entity as if combination occurred at beginning of period | 1,120,000,000 |  |  |  |  |  |
Profit (loss) of combined entity as if combination occurred at beginning of period | 46,000,000 |  |  |  |  |  |
Novatec Holding GmbH |  |  |  |  |  |  |
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Number of professionals employed | employee |  |  |  | 300 |  |  |
Momentum Technologies Inc. |  |  |  |  |  |  |
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Number of professionals employed | employee |  |  | 250 |  |  |  |
Apside |  |  |  |  |  |  |
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Net assets acquired | 229,890,000 | $ 229,890,000 |  |  |  |  |
Number of professionals employed | employee |  | 2,500 |  |  |  |  |
Revenue of acquiree since acquisition date | 32,000,000 |  |  |  |  |  |
Profit (loss) of acquiree since acquisition date | 0 |  |  |  |  |  |
Revenue of combined entity as if combination occurred at beginning of period | 1,120,000,000 |  |  |  |  |  |
Profit (loss) of combined entity as if combination occurred at beginning of period | 46,000,000 |  |  |  |  |  |
Aeyon |  |  |  |  |  |  |
Disclosure of detailed information about business combination [line items] |  |  |  |  |  |  |
Net assets acquired |  |  |  |  |  |  | $ 317,841,000
Increase (decrease) in goodwill | $ 47,507,000 |  |  |  |  |  |

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