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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