Commitments and Contingencies (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Letters of Credit Outstanding, Amount	$ 53.3
Special Assessment Bond	632.7
Lessee, Operating Lease, Liability, to be Paid, Year Five	0.2
Land purchase contract deposits	10.0	$ 10.4
Purchase Obligation	490.3
Operating Lease, Expense	2.5	$ 1.7	$ 1.1
Lessee, Operating Lease, Liability, to be Paid, Year One	2.4
Lessee, Operating Lease, Liability, to be Paid, Year Two	2.4
Lessee, Operating Lease, Liability, to be Paid, Year Three	1.9
Lessee, Operating Lease, Liability, to be Paid, Year Four	1.4
Lessee, Operating Lease, Liability, to be Paid, after Year Five	$ 0.0