CONSOLIDATION AND BASIS OF PRESENTATION - GP Units (UNITED DOMINION REALTY, L.P.) (Details)	12 Months Ended
	Dec. 31, 2019 home USD ($) community item shares	Dec. 31, 2018 shares	Dec. 31, 2017 shares	Dec. 31, 2016 shares
Basis of presentation
Number of real estate properties | community	148
Number of markets operating within (in markets) | $	20
Number of apartments owned (in apartments homes) | home	47,010
Operating Partnership outstanding units	184,100,000	183,600,000
Operating Partnership units outstanding related to limited partner	184,064,000	183,637,000	183,351,000	183,279,000
United Dominion Realty L.P.
Basis of presentation
Operating Partnership units outstanding related to limited partner	176,200,000	174,200,000
Percentage of units outstanding in Partnership	95.70%	94.90%
United Dominion Realty L.P.
Basis of presentation
Rental revenues percent of General Partner's consolidated rental revenues	39.00%	42.00%	43.00%
Number of real estate properties | community	52
Number of markets operating within (in markets) | item	15
Number of apartments owned (in apartments homes) | home	16,434
Operating Partnership outstanding units	184,100,000	183,600,000
OP units outstanding related to general partner	110,883	110,883
Operating Partnership units outstanding related to limited partner	183,952,659	183,525,660
UDR, Inc.
Basis of presentation
General Partners' ownership (as a percent)	56.80%
Operating Partnership outstanding units	18,400,000	17,200,000
Operating Partnership units outstanding related to limited partner	176,100,000	174,100,000
Percentage of units outstanding in Partnership	95.70%	94.90%
UDR, Inc. | United Dominion Realty L.P.
Basis of presentation
General Partners' ownership (as a percent)	95.70%	94.90%
Operating Partnership outstanding units	176,200,000	174,200,000
OP units outstanding related to general partner	100,000	100,000
Percentage of total outstanding Operating Partnership units represented by General Partnership units outstanding	0.10%	0.10%
Operating Partnership units outstanding related to limited partner	176,100,000	174,100,000
Percentage of units outstanding in Partnership	95.70%	94.80%
Non-affiliated Partners
Basis of presentation
Operating Partnership outstanding units	14,000,000.0	9,400,000
Operating Partnership units outstanding related to limited partner	7,900,000
Percentage of units outstanding in Partnership	4.30%	5.10%
Non-affiliated Partners | United Dominion Realty L.P.
Basis of presentation
Operating Partnership outstanding units	7,900,000	9,400,000
Operating Partnership units outstanding related to limited partner	7,900,000
Percentage of units outstanding in Partnership	4.30%	5.10%
Class A Limited Partner | United Dominion Realty L.P.
Basis of presentation
Operating Partnership units outstanding related to limited partner	1,900,000	1,900,000
Class A Limited Partner | UDR, Inc.
Basis of presentation
Operating Partnership units outstanding related to limited partner	121,000	121,000	121,000	121,000
Non-affiliated Partners | United Dominion Realty L.P.
Basis of presentation
Operating Partnership units outstanding related to limited partner	7,900,000	9,400,000
Percentage of units outstanding in Partnership	4.30%	5.10%
Non-affiliated Partners | Class A Limited Partner
Basis of presentation
Operating Partnership units outstanding related to limited partner	1,752,000	1,752,000	1,752,000	1,752,000