Inventory (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Inventory [Line Items]
Carrying Value of Communities with Impairment Indicators	$ 30.6		$ 30.6
Impairment charges	9.2	$ 3.8	14.0	$ 3.8
Write-offs (recoveries) of earnest money deposits and pre-acquisition costs	$ 14.6	$ 11.4	$ 37.4	$ 16.2