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Real Estate - Text (Detail) - USD ($) $ in Millions	3 Months Ended
Real Estate - Text (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Sep. 30, 2024
Real Estate Properties [Line Items]
Real estate	$ 2,736.8		$ 2,266.2
Asset Impairment Charges	0.0	$ 0.0
Loss on Contract Termination	1.1	$ 0.2
Payments to Develop Real Estate Assets	297.0
Payments to Acquire Residential Real Estate	387.4
Developed and under development projects
Real Estate Properties [Line Items]
Real estate	2,484.1		2,126.1
Land held for future development
Real Estate Properties [Line Items]
Real estate	$ 252.7		$ 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%