Owned Inventory - Narrative (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2025 USD ($) home	Mar. 31, 2024 USD ($)	Mar. 31, 2025 USD ($) home	Mar. 31, 2024 USD ($)	Sep. 30, 2024 USD ($) home
Inventory Disclosure [Abstract]
Number of homes under construction | home	2,555		2,555		2,315
Number of homes under construction, spec homes | home	1,306		1,306		1,154
Total, spec homes	$ 414,700,000		$ 414,700,000		$ 360,900,000
Number of homes under construction, in-process spec homes | home	1,019		1,019		827
In-process spec homes	$ 295,300,000		$ 295,300,000		$ 231,400,000
Number of homes under construction, finished spec homes | home	287		287		327
Finished spec homes	$ 119,400,000		$ 119,400,000		$ 129,500,000
Threshold number of homes below a minimum threshold of profitability | home			10
Impairment of projects in process	0	$ 0	$ 0	$ 0
Impairment charges on land held for sale	0	0	0	0
Abandonments charges	$ 528,000	$ 0	$ 528,000	$ 0