Stock-based Compensation - Compensation Cost of Share-based Compensation Arrangements (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Total compensation cost	$ 7.8	$ 6.6	$ 11.2
Compensation cost capitalized	(1.1)	(0.8)	(1.4)
Compensation cost recognized in net income	6.7	5.8	9.8
Income tax benefit recognized in net income	(1.5)	(1.3)	(2.2)
Compensation cost recognized in net income, net of income tax	$ 5.2	$ 4.5	$ 7.6