Property and Equipment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	$ 367.0		$ 367.0		$ 683.7
Depreciation	14.7	$ 17.1	49.5	$ 51.6
Rental properties	722.3		722.3		0.0
Intersegment Eliminations [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	0.0		0.0		(3.0)
Rental properties	(17.1)		(17.1)
Other Segments [Member]
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(26.6)		(26.6)		(28.2)
Property, Plant and Equipment, Net	81.1		81.1		308.9
Other Segments [Member] | Multifamily [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross					232.1
Rental properties	436.3		436.3
Other Segments [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	16.5		16.5		15.6
Other Segments [Member] | Other Assets [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	75.1		75.1		69.7
Other Segments [Member] | LandMember
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	16.1		16.1		19.7
Forestar Group [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	2.2		2.2		1.1
Rental properties	0.0		0.0
Financial Services [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	3.4		3.4		3.9
Rental properties	0.0		0.0
HomeBuildingMember
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(268.4)		(268.4)		(256.2)
Property, Plant and Equipment, Net	280.3		280.3		372.8
HomeBuildingMember | Single Family [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross					87.2
Rental properties	303.1		303.1
HomeBuildingMember | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	277.0		277.0		267.4
HomeBuildingMember | 2510 Household Furniture [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	133.9		133.9		134.0
HomeBuildingMember | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	105.6		105.6		108.1
HomeBuildingMember | LandMember
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	32.2		32.2		32.3
MultifamilyMember
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	0.0		0.0		232.1
MultifamilyMember | LandMember
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	0.0		0.0		58.3
MultifamilyMember | Property, Plant and Equipment, Other Types
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	0.0		0.0		173.8
SingleFamilyMember
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	0.0		0.0		87.2
SingleFamilyMember | LandMember
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	0.0		0.0		19.1
SingleFamilyMember | Property, Plant and Equipment, Other Types
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 0.0		$ 0.0		$ 68.1