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Real Estate - Text (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Real Estate - Text (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Sep. 30, 2023
Real Estate Properties [Line Items]
Real estate	$ 2,238.7		$ 2,238.7		$ 1,790.3
Payments to Acquire Residential Real Estate			441.4
Payments to Develop Real Estate Assets			730.2
Asset Impairment Charges	0.0		0.0	$ 19.4
Loss on Contract Termination	0.7	$ 0.9	1.0	$ 4.2
Developed and under development projects
Real Estate Properties [Line Items]
Real estate	2,103.3		2,103.3		1,760.8
Land held for future development
Real Estate Properties [Line Items]
Real estate	$ 135.4		$ 135.4		$ 29.5
D.R. Horton, Inc. [Member] \| Maximum
Real Estate Properties [Line Items]
Related Party Transaction, Rate			16.00%
D.R. Horton, Inc. [Member] \| Minimum
Real Estate Properties [Line Items]
Related Party Transaction, Rate			12.00%