Income Taxes -Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Effective income tax rate	21.20%	25.20%	20.20%	13.70%
Unrecognized tax benefits, uncertain tax positions	$ 13.2		$ 13.2		$ 10.9
Unrecognized tax benefits, accrued interest	$ 0.6		$ 0.6		$ 0.4