Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Income tax expense	$ 5.4	$ 1.0
Effective income tax rate, percent	24.00%	21.00%
Deferred Tax Assets, Net Of Deferred Tax Liabilities	$ 15.1		$ 20.7
Valuation allowance, deferred tax asset, amount	3.3		$ 3.3
Unrecognized tax benefits	$ 1.3