Commitments and Contingencies - Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating Leases [Abstract]
Operating Leases, Rent Expense	$ 12.0	$ 11.3	$ 9.9
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	10.1
Operating Leases, Future Minimum Payments, Due in Two Years	9.3
Operating Leases, Future Minimum Payments, Due in Three Years	8.1
Operating Leases, Future Minimum Payments, Due in Four Years	5.8
Operating Leases, Future Minimum Payments, Due in Five Years	4.5
Operating Leases, Future Minimum Payments, Due Thereafter	5.6
Operating Leases, Future Minimum Payments Due	$ 43.4