Inventory - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021 USD ($) home	Dec. 31, 2020 USD ($) contract	Mar. 31, 2021 USD ($) home	Sep. 30, 2020 USD ($) home
Inventory Disclosure [Abstract]
Number of substantially completed homes unsold | home	87		87	133
Total value of substantially completed homes | $	$ 26.2		$ 26.2	$ 42.2
Threshold number of homes below a minimum threshold of profitability | home			10
Impairment charges, abandonments | $	$ 0.0	$ 0.5	$ 0.0
Number of terminated land contracts under acquisition | contract		1