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Real Estate - Text (Detail) - USD ($) $ in Millions	3 Months Ended
Real Estate - Text (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Sep. 30, 2025
Real Estate Properties [Line Items]
Real estate	$ 2,850.5		$ 2,645.1
Payments to Acquire Residential Real Estate	110.1
Payments to Develop Real Estate Assets	304.6
Asset Impairment Charges	0.0	$ 0.0
Loss on Contract Termination	0.8	$ 1.1
Developed and under development projects
Real Estate Properties [Line Items]
Real estate	2,676.9		2,465.1
Land held for future development
Real Estate Properties [Line Items]
Real estate	$ 173.6		$ 180.0
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%