Leases - Summary of Total Lease Costs and Other Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Lease cost:
Operating lease cost	$ 25,185	$ 25,396
Short-term lease cost	826	775
Variable lease cost	5,867	5,255
Total lease cost	31,878	31,426
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	24,894	24,943
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 15,894	$ 20,487