Inventory (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Carrying value of communities with impairment indicators	$ 33.5
Impairment charges	5.6	$ 0.0
Write-offs (recoveries) of earnest money deposits and pre-acquisition costs	$ 2.7	$ 3.8