Revenue Recognition - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Revenue Recognition [Line Items]
Contract costs, amortization period	5 years
Contract liabilities	$ 139.9		$ 139.6
Contract with customer liability, revenue recognized	$ 70.2	$ 71.5
Maximum
Revenue Recognition [Line Items]
Contract liabilities recognition service contract period	1 year
Delivery and Branch Expenses
Revenue Recognition [Line Items]
Amortization of deferred contract costs	$ 1.0	$ 1.0
Prepaid Expense and Other Current Assets
Revenue Recognition [Line Items]
Deferred contract costs,current	3.5		3.4
Deferred Charges and Other Assets, Net
Revenue Recognition [Line Items]
Deferred contract costs,non current	$ 6.3		$ 5.9