Condensed Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Foreign Currency Translation Adjustments	Treasury Stock, Common
Stockholders' Equity, beginning of period at Sep. 30, 2023		$ 1.4	$ 19.3	$ (190.1)	$ (3.1)	$ (151.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Activity under stock and deferred compensation plans			(3.2)
Non-cash stock-based compensation expense			15.5
Net earnings	$ 174.8			174.8
Foreign currency translation adjustments					0.3
Purchases of treasury stock	107.1					(107.1)
Stockholders' Equity, end of period at Jun. 30, 2024	(243.2)	1.4	31.6	(15.3)	(2.8)	(258.1)
Stockholders' Equity, beginning of period at Mar. 31, 2024		1.4	26.1	(89.0)	(2.7)	(183.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Activity under stock and deferred compensation plans			0.0
Non-cash stock-based compensation expense			5.5
Net earnings	73.7			73.7
Foreign currency translation adjustments					(0.1)
Purchases of treasury stock	74.6					(74.6)
Stockholders' Equity, end of period at Jun. 30, 2024	(243.2)	1.4	31.6	(15.3)	(2.8)	(258.1)
Stockholders' Equity, beginning of period at Sep. 30, 2024	(205.9)	1.4	37.3	56.4	(2.0)	(299.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Activity under stock and deferred compensation plans			(11.0)
Non-cash stock-based compensation expense			16.9
Net earnings	156.6			156.6
Foreign currency translation adjustments					1.1
Purchases of treasury stock	267.6					(267.6)
Stockholders' Equity, end of period at Jun. 30, 2025	(309.9)	1.4	43.2	213.0	(0.9)	(566.6)
Stockholders' Equity, beginning of period at Mar. 31, 2025		1.4	37.9	192.0	(2.7)	(482.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Activity under stock and deferred compensation plans			0.1
Non-cash stock-based compensation expense			5.2
Net earnings	21.0			21.0
Foreign currency translation adjustments					1.8
Purchases of treasury stock	83.9					(83.9)
Stockholders' Equity, end of period at Jun. 30, 2025	$ (309.9)	$ 1.4	$ 43.2	$ 213.0	$ (0.9)	$ (566.6)