Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Product and Service, Revenue [Line Items]
Residential lot sales	$ 331.4	$ 346.9	$ 566.6	$ 594.2
Tract sales and other	42.9	4.1	80.7	7.1
Revenues	$ 374.3	$ 351.0	$ 647.3	$ 601.3