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Property and Equipment (Details) $ in Millions	3 Months Ended		9 Months Ended
Property and Equipment (Details) $ in Millions	Jun. 30, 2020 USD ($) Projects	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Projects	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 920.6		$ 920.6		$ 760.1
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(288.7)		(288.7)		(260.9)
Property, Plant and Equipment, Net	631.9		631.9		499.2
Depreciation	17.1	$ 16.7	51.6	$ 48.4
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	349.7		349.7		329.4
2510 Household Furniture [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	136.4		136.4		128.3
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	129.1		129.1		128.6
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	100.3		100.3		71.6
Oil and Gas Properties [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	65.1		65.1		56.9
Multifamily [Member] \| Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	86.2		86.2		65.2
Multifamily [Member] \| Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	60.0		60.0		38.0
Multifamily [Member] \| Other Property [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	63.5		63.5		50.7
Other Segments [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	284.8		284.8		221.2
Single Family [Member] \| Assets Leased to Others [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 118.9		$ 118.9		$ 37.0
Multifamily [Member] \| Other Segments [Member] \| Asset under Construction [Member]
Property, Plant and Equipment [Line Items]
Number of Projects \| Projects	4		4
Multifamily [Member] \| Other Segments [Member] \| Assets Leased to Others [Member]
Property, Plant and Equipment [Line Items]
Number of Projects \| Projects	1		1