REAL ESTATE OWNED (UNITED DOMINION REALTY, L.P.) - Acquisitions and Dispositions (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) state community item	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) state community item	Sep. 30, 2017 USD ($)
Real Estate Owned Disclosure
Number of communities owned (in communities) | community	127		127
Number of states in which there are owned and consolidated communities | state	11		11
Development costs excluding direct costs and capitalized interest	$ 1.6	$ 2.2	$ 6.6	$ 6.6
Number of apartments owned (in apartments homes) | item	40,420		40,420
Interest capitalized during period	$ 1.6	4.6	$ 9.8	14.0
United Dominion Reality L.P.
Real Estate Owned Disclosure
Number of communities owned (in communities) | community	52		52
Number of states in which there are owned and consolidated communities | state	9		9
Development costs excluding direct costs and capitalized interest	$ 0.0			0.4
Number of apartments owned (in apartments homes) | item	16,434		16,434
United Dominion Reality L.P. | Maximum
Real Estate Owned Disclosure
Development costs excluding direct costs and capitalized interest		0.1	$ 0.1
Interest capitalized during period	$ 0.1	$ 0.1	$ 0.1	$ 0.1