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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Property and Equipment (Details) $ in Millions	3 Months Ended		6 Months Ended
Property and Equipment (Details) $ in Millions	Mar. 31, 2020 USD ($) Projects	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) Projects	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 865.2		$ 865.2		$ 760.1
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(275.5)		(275.5)		(260.9)
Property, Plant and Equipment, Net	589.7		589.7		499.2
Depreciation	17.3	$ 15.9	34.5	$ 31.7
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	335.7		335.7		329.4
2510 Household Furniture [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	134.5		134.5		128.3
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	126.0		126.0		128.6
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	91.9		91.9		71.6
Oil and Gas Properties [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	63.6		63.6		56.9
Multifamily [Member] \| Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	75.5		75.5		65.2
Multifamily [Member] \| Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	55.1		55.1		38.0
Multifamily [Member] \| Other Property [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	53.1		53.1		50.7
Other Segments [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Net	259.2		259.2		221.2
Single Family [Member] \| Assets Leased to Others [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 101.6		$ 101.6		$ 37.0
Multifamily [Member] \| Other Segments [Member] \| Asset under Construction [Member]
Property, Plant and Equipment [Line Items]
Number of Projects \| Projects	3		3
Multifamily [Member] \| Other Segments [Member] \| Assets Leased to Others [Member]
Property, Plant and Equipment [Line Items]
Number of Projects \| Projects	1		1