Income Taxes -Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Effective income tax rate	(1.60%)	7.30%
Unrecognized tax benefits, uncertain tax positions	$ 20.7		$ 19.9
Unrecognized tax benefits, accrued interest	$ 2.0		$ 1.7