Leases - Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Operating lease cost:
Operating lease cost	$ 74,086	$ 67,414	$ 61,980
Variable lease cost	16,315	15,229	13,000
Total operating lease cost	90,401	82,643	74,980
Financing lease cost:
Amortization of financing lease assets	327	3	0
Interest on financing lease liabilities	145	1	0
Total financing lease cost	472	4	0
Total lease cost	90,873	82,647	74,980
Sublease rental income	$ 3,700	$ 3,600	$ 3,400
Weighted-average remaining lease term (years):
Operating leases	4 years 11 months 19 days	5 years 1 month 13 days
Financing leases	3 years 8 months 1 day	4 years 1 month 6 days
Weighted-average discount rate:
Operating leases	8.51%	8.32%
Financing leases	11.14%	11.14%