Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Eligible employees contribution to 401(k) plan (up to 25%)	25.00%
Employer contributions into 401(k) plans	$ 9.8	$ 10.1	$ 10.3
Employee incentive plans expenses	$ 58.1	$ 60.6	$ 57.5