Income Taxes - Current and Deferred Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Current taxes:
U.S. federal	$ 8.2	$ 6.7	$ (0.6)
U.S. state and local	3.6	(0.1)	2.3
Total current taxes	70.4	34.6	33.0
Deferred taxes:
U.S. federal	3.4	1.4	4.9
U.S. state and local	(0.1)	2.7	0.6
Total deferred taxes	(0.3)	3.2	4.1
Income tax expense	70.1	37.8	37.1
Australia
Current taxes:
Foreign tax expense	2.8	1.8	0.5
Deferred taxes:
Other international	(0.2)	0.3	(0.1)
Brazil
Current taxes:
Foreign tax expense	12.6	8.0	6.5
Deferred taxes:
Other international	(0.8)	(1.3)	(1.3)
Germany
Current taxes:
Foreign tax expense	8.9	6.0	3.4
Singapore
Current taxes:
Foreign tax expense	2.0	1.9	2.8
Deferred taxes:
Other international	0.0	0.4	0.8
United Kingdom
Current taxes:
Foreign tax expense	29.2	6.6	13.9
Deferred taxes:
Other international	(2.7)	0.1	(0.3)
Other international
Current taxes:
Foreign tax expense	3.1	3.7	4.2
Deferred taxes:
Other international	$ 0.1	$ (0.4)	$ (0.5)