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Real Estate - Text (Detail) - USD ($) $ in Millions	12 Months Ended
Real Estate - Text (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Real Estate Properties [Line Items]
Real estate	$ 2,645.1	$ 2,266.2
Payments to Acquire Residential Real Estate	595.3
Payments to Develop Real Estate Assets	1,100.0
Asset Impairment Charges	0.0	0.0	$ 19.4
Loss on Contract Termination	7.2	4.1	$ 4.6
Developed and under development projects
Real Estate Properties [Line Items]
Real estate	2,465.1	2,126.1
Land held for future development
Real Estate Properties [Line Items]
Real estate	$ 180.0	$ 140.1
D.R. Horton, Inc. [Member] \| Minimum
Real Estate Properties [Line Items]
Related Party Transaction, Rate	12.00%
D.R. Horton, Inc. [Member] \| Maximum
Real Estate Properties [Line Items]
Related Party Transaction, Rate	16.00%