Inventory (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Inventory [Line Items]
Impairment charges	$ 0.0	$ 1.7	$ 5.6	$ 1.7
Write-offs (recoveries) of earnest money deposits and pre-acquisition costs	$ 3.8	$ 7.2	$ 6.5	$ 11.1