Property and Equipment (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	$ 748.4		$ 683.7
Depreciation	17.8	$ 17.2
Intersegment Eliminations [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	(4.6)		(3.0)
Multifamily [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	281.2		232.1
Multifamily [Member] | Assets Leased to Others [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	204.2		173.8
Multifamily [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	77.0		58.3
Other Segments [Member]
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(27.1)		(28.2)
Property, Plant and Equipment, Net	359.1		308.9
Other Segments [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	16.1		15.6
Other Segments [Member] | Other Assets [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	69.2		69.7
Other Segments [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	19.7		19.7
Single Family [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	106.6		87.2
Single Family [Member] | Assets Leased to Others [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	89.3		68.1
Single Family [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	17.3		19.1
Home Building [Member]
Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(266.6)		(256.2)
Property, Plant and Equipment, Net	388.3		372.8
Home Building [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	272.7		267.4
Home Building [Member] | 2510 Household Furniture [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	134.4		134.0
Home Building [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	109.4		108.1
Home Building [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	31.8		32.3
Forestar Group [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	1.9		1.1
Financial Services [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	$ 3.7		$ 3.9