Commitments and Contingencies - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Loss Contingencies [Line Items]
Total rental expense for operating leases	$ 250,400,000	$ 249,800,000	$ 242,000,000.0
Outstanding letters of credit	18,000,000.0	18,700,000
Data security incidents, remaining liability	$ 0	14,294,000
Data security incidents
Loss Contingencies [Line Items]
Data security incident expenses		$ 7,900,000