Owned Inventory - Narrative (Details)	12 Months Ended
	Sep. 30, 2024 USD ($) home	Sep. 30, 2023 USD ($) home	Sep. 30, 2022 USD ($) community
Segment Reporting Information [Line Items]
Number of homes under construction | home	2,315	2,163
Number of homes under construction, spec homes | home	1,154	779
Total, spec homes	$ 360,900,000	$ 218,000,000.0
Number of homes under construction, in-process spec homes | home	827	645
In-process spec homes	$ 231,400,000	$ 162,000,000.0
Number of homes under construction, finished spec homes | home	327	134
Finished spec homes	$ 129,500,000	$ 56,000,000.0
Threshold number of homes below a minimum threshold of profitability | home	10
Impairment of projects in process	$ 0	0	$ 0
Land held for sale	0	0	1,868,000
Fair value of impaired long-lived assets to be disposed of			900,000
Abandonments	$ 1,996,000	$ 641,000	$ 1,095,000
West
Segment Reporting Information [Line Items]
Number of communities | community			2