Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, net
Beginning balance at Sep. 30, 2021	$ 904.0	$ 0.2	$ (69.3)	$ 315.7	$ 682.5	$ (25.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	154.8				154.8
Other comprehensive gain (loss), net of tax	(30.5)					(30.5)
Exercise of stock options	6.2			6.2
Share-based compensation	12.8			12.8
Ending balance at Jun. 30, 2022	1,047.3	0.2	(69.3)	334.7	837.3	(55.6)
Beginning balance at Mar. 31, 2022	1,005.6	0.2	(69.3)	329.9	788.2	(43.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	49.1				49.1
Other comprehensive gain (loss), net of tax	(12.2)					(12.2)
Exercise of stock options	0.3			0.3
Share-based compensation	4.5			4.5
Ending balance at Jun. 30, 2022	1,047.3	0.2	(69.3)	334.7	837.3	(55.6)
Beginning balance at Sep. 30, 2022	1,070.1	0.2	(69.3)	340.2	889.6	(90.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	187.8				187.8
Other comprehensive gain (loss), net of tax	47.1					47.1
Exercise of stock options	3.6			3.6
Share-based compensation	21.3			21.3
Ending balance at Jun. 30, 2023	1,329.9	0.2	(69.3)	365.1	1,077.4	(43.5)
Beginning balance at Mar. 31, 2023	1,247.3	0.2	(69.3)	358.7	1,007.9	(50.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	69.5				69.5
Other comprehensive gain (loss), net of tax	6.7					6.7
Exercise of stock options	0.0			0.0
Share-based compensation	6.4			6.4
Ending balance at Jun. 30, 2023	$ 1,329.9	$ 0.2	$ (69.3)	$ 365.1	$ 1,077.4	$ (43.5)