Income Taxes - U.S. and International Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Income from operations, before tax	$ 206.7	$ 111.0	$ 101.5
United States [Member]
Operating Loss Carryforwards [Line Items]
U.S.	88.8	(2.6)	9.9
Non-US [Member]
Operating Loss Carryforwards [Line Items]
International	$ 117.9	$ 113.6	$ 91.6