Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, net
Beginning balance at Sep. 30, 2022	$ 1,070.1	$ 0.4	$ (69.3)	$ 340.0	$ 889.6	$ (90.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	76.6				76.6
Other comprehensive gain (loss), net of tax	22.9					22.9
Exercise of stock options	1.5			1.5
Share-based compensation	5.5			5.5
Ending balance at Dec. 31, 2022	1,176.6	0.4	(69.3)	347.0	966.2	(67.7)
Beginning balance at Sep. 30, 2023	1,379.1	0.4	(69.3)	371.7	1,128.1	(51.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	69.1				69.1
Other comprehensive gain (loss), net of tax	27.6					27.6
Exercise of stock options	0.5			0.5
Shares withheld to cover taxes on vesting of equity awards	(1.1)			(1.1)
Share-based compensation	7.6			7.6
Ending balance at Dec. 31, 2023	$ 1,482.8	$ 0.4	$ (69.3)	$ 378.7	$ 1,197.2	$ (24.2)