Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Operating Leased Assets [Line Items]
Operating leases rent expense	$ 46.9	$ 43.9	$ 36.7
Facilities
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	15.2
Facilities | Minimum
Operating Leased Assets [Line Items]
Annual sublease income	3.1
Facilities | Maximum
Operating Leased Assets [Line Items]
Annual sublease income	$ 2.4