Annual report [Section 13 and 15(d), not S-K Item 405]

Fair Value Measurements - Narrative (Details)

v3.25.3
Fair Value Measurements - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2023
Sep. 30, 2022
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]        
Performance bond commitments $ 33,200      
Shareholders' equity 1,674,035 $ 1,842,815 $ 1,667,835 $ 1,549,371
Foreign currency translation adjustment        
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]        
Shareholders' equity (20,706) (39,225) (50,484) $ (57,109)
British Pound | Foreign currency translation adjustment        
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]        
Shareholders' equity 12,600      
Canadian Dollars | Foreign currency translation adjustment        
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]        
Shareholders' equity 7,600      
U.S. Services and Outside the U.S. Services        
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]        
Impairment of long-lived assets held-for-use $ 0 $ 0 $ 9,500  
Impairment, Long-Lived Asset, Held-for-Use, Statement of Income or Comprehensive Income [Extensible Enumeration]     Amortization of intangible assets