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DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair value of financial instruments (Details) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands | 12 Months Ended |
--- | --- | ---
Sep. 30, 2025 USD ($) $ / shares | Sep. 30, 2025 CAD ($) $ / shares | Sep. 30, 2024 USD ($) $ / shares | Sep. 30, 2023 USD ($) | Sep. 30, 2025 CAD ($)
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax | $ (6,569) |  | $ 10,137 |  |
Defined benefit plan, fair value of plan assets | 132,376 |  | 158,705 |  |
Prepaid Expenses and Other Current Assets |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Fair value of insurance contracts | 5,249 |  |  |  |
Pension Plan |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Defined benefit plan, fair value of plan assets | 132,376 |  | 158,705 | $ 146,997 |
Australian Dollar Contracts | Designated as hedging instrument |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Derivative, notional amount | $ 41,000 |  | $ 67,500 |  |
Contracts weighted average rate price (in dollars per share) | $ / shares | $ 1.50 |  | $ 1.47 |  |
Accumulated other comprehensive income (loss), foreign currency translation adjustment, before tax | $ 698 |  | $ (660) |  |
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax | 489 |  | (462) |  |
Gain (loss) on hedging activity | $ 2,919 |  | 1,120 | 3,991 |
Australian Dollar Contracts | Designated as hedging instrument | Maximum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 90 days | 90 days |  |  |
Australian Dollar Contracts | Designated as hedging instrument | Minimum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 30 days | 30 days |  |  |
Chinese Yuan Contracts | Designated as hedging instrument |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Derivative, notional amount | $ 21,000 |  | $ 20,500 |  |
Contracts weighted average rate price (in dollars per share) | $ / shares | $ 7.10 |  | $ 7.11 |  |
Accumulated other comprehensive income (loss), foreign currency translation adjustment, before tax | $ 37 |  | $ (410) |  |
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax | 27 |  | 300 |  |
Gain (loss) on hedging activity | $ (974) |  | (1,936) | (2,313) |
Chinese Yuan Contracts | Designated as hedging instrument | Maximum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 273 days | 273 days |  |  |
Chinese Yuan Contracts | Designated as hedging instrument | Minimum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 31 days | 31 days |  |  |
Canadian Dollar Contract | Designated as hedging instrument |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Contracts weighted average rate price (in dollars per share) | $ / shares |  | $ 5.17 |  |  |
Canadian Dollar Contract | Designated as hedging instrument | Maximum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 359 days | 359 days |  |  |
Canadian Dollar Contract | Designated as hedging instrument | Minimum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 30 days | 30 days |  |  |
Canadian Dollar Contract | Not Designated as Hedging Instrument |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Derivative, notional amount | $ 6,150 |  | $ 13,497 |  | $ 1,742
Contracts weighted average rate price (in dollars per share) | $ / shares | $ 1.40 |  | $ 1.35 |  |
Fair value gain (loss) on foreign currency contract not qualify for hedge accounting | $ (100) | $ 15 | $ (67) |  |
Canadian Dollar Contract | Not Designated as Hedging Instrument | Maximum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 330 days | 330 days |  |  |
Canadian Dollar Contract | Not Designated as Hedging Instrument | Minimum |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Term of contract | 2 days | 2 days |  |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Term Loan B due 2029 |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Long-term debt, fair value | $ 450,684 |  |  |  |
Significant Other Observable Inputs (Level 2) | Canadian Dollar Contract | Not Designated as Hedging Instrument | Other Income |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Gain (loss) on sale of derivatives | 157 |  | $ 98 | $ 336 |
Senior Notes due 2028 | Quoted Prices in Active Markets for Identical Assets (Level 1) | Senior Notes |  |  |  |  |
Description Of Business And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Long-term debt, fair value | $ 972,338 |  |  |  |

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