Income Taxes - Current and Deferred Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Current taxes:
U.S. federal	$ 6.7	$ (0.6)	$ (1.9)
U.S. state and local	(0.1)	2.3	(0.8)
Total current taxes	34.6	33.0	22.2
Deferred taxes:
U.S. federal	1.4	4.9	1.6
U.S. state and local	2.7	0.6	0.4
Total deferred taxes	3.2	4.1	3.7
Income tax expense	37.8	37.1	25.9
Australia
Current taxes:
Foreign tax expense	1.8	0.5	0.0
Deferred taxes:
Other international	0.3	(0.1)	0.1
Brazil
Current taxes:
Foreign tax expense	8.0	6.5	5.5
Deferred taxes:
Other international	(1.3)	(1.3)	0.0
Germany
Current taxes:
Foreign tax expense	6.0	3.4	0.1
Singapore
Current taxes:
Foreign tax expense	1.9	2.8	0.0
Deferred taxes:
Other international	0.4	0.8	2.5
United Kingdom
Current taxes:
Foreign tax expense	6.6	13.9	17.2
Deferred taxes:
Other international	0.1	(0.3)	(0.5)
Other international
Current taxes:
Foreign tax expense	3.7	4.2	2.1
Deferred taxes:
Other international	$ (0.4)	$ (0.5)	$ (0.4)