v3.26.1
Goodwill and Intangible Assets, net - Intangible Assets Subject to Amortization (Detail) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Finite Lived Intangible Assets [Line Items]    
Gross Carrying Amount $ 546,644 $ 545,459
Accum. Amortization 434,690 420,567
Net 111,954 124,892
Customer Lists    
Finite Lived Intangible Assets [Line Items]    
Gross Carrying Amount 493,431 493,431
Accum. Amortization 404,196 391,702
Net 89,235 101,729
Trade Names And Other Intangibles    
Finite Lived Intangible Assets [Line Items]    
Gross Carrying Amount 53,213 52,028
Accum. Amortization 30,494 28,865
Net $ 22,719 $ 23,163