Inventory - Narrative (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2020 USD ($) home Community	Mar. 31, 2019 USD ($) Community	Mar. 31, 2020 USD ($) home Community	Mar. 31, 2019 USD ($) Community	Sep. 30, 2019 USD ($) home
Inventory Disclosure [Abstract]
Number of substantially completed homes unsold | home	243		243		238
Total value of substantially completed homes	$ 80,500,000		$ 80,500,000		$ 82,200,000
Threshold number of homes below a minimum threshold of profitability | home			10
Number of communities on watch list | Community	3	12	3	12
Impairment charge				$ 109,000,000
Inventory impairments and abandonments	$ 0	$ 147,611,000	$ 0	$ 148,618,000
Number of impaired communities | Community				9
Impairment of land held for sale		$ 38,600,000.0		$ 38,588,000
Number of properties included in land held for sale | Community				6