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Accounting Policies (Details) $ in Millions				9 Months Ended	12 Months Ended
Accounting Policies (Details) $ in Millions	Sep. 30, 2020 USD ($)	Feb. 08, 2018 USD ($) a Lot Project	Oct. 05, 2017	Sep. 30, 2018 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Oct. 01, 2019 USD ($)
Accounting Policies [Abstract]
Operating Lease, Right-of-Use Asset	$ 3.6				$ 3.6	$ 0.0	$ 2.7
Operating Lease, Liability	3.8				3.8	0.0	$ 2.9
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2.3				2.3	4.3
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1.2)				(1.2)	(1.9)
Property and equipment, net	$ 1.1				1.1	2.4
Depreciation				$ 0.2	0.3	0.3
D.R. Horton, Inc. [Member] \| Majority Shareholder [Member]
Accounting Policies [Abstract]
Sale of Stock, Percentage of Ownership after Transaction	65.00%		75.00%
Property, Plant and Equipment [Line Items]
Sale of Stock, Percentage of Ownership after Transaction	65.00%		75.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Projects Sold \| Project		24
Disposal Group, Including Discontinued Operation, Consideration		$ 232.0
Proceeds from Sale of Real Estate		$ 217.5
Property, Plant and Equipment [Line Items]
Number of Projects Sold \| Project		24
Disposal Group, Including Discontinued Operation, Consideration		$ 232.0
Proceeds from Sale of Real Estate		$ 217.5
Multifamily [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Projects Sold \| Project		1
Property, Plant and Equipment [Line Items]
Number of Projects Sold \| Project		1
Residential Real Estate [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Lots \| Lot		750
Property, Plant and Equipment [Line Items]
Number of Lots \| Lot		750
Land and Land Improvements [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Lots \| Lot		4,000
Property, Plant and Equipment [Line Items]
Number of Lots \| Lot		4,000
Land [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Area of Land \| a		730
Property, Plant and Equipment [Line Items]
Area of Land \| a		730
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1.2				1.2	0.9
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1.1				$ 1.1	$ 3.4
Maximum \| Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					10 years
Maximum \| Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					10 years
Minimum \| Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					5 years
Minimum \| Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					2 years