Leases - Summary of Total Lease Costs and Other Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Lease cost:
Operating lease cost	$ 27,840	$ 25,294	$ 23,637
Short-term lease cost	622	754	818
Variable lease cost	5,673	6,153	5,598
Total lease cost	34,135	32,201	30,053
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	28,262	25,504	23,622
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 23,887	$ 20,619	$ 15,994
Weighted-average remaining lease term - operating leases	5 years 4 months 24 days	5 years 3 months 18 days	5 years 7 months 6 days
Weighted-average discount rate - operating leases	6.60%	6.30%	5.90%