CAPITAL STRUCTURE (UNITED DOMINION REALTY, L.P.) - Ownership Interests (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) class $ / shares shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 shares	Dec. 31, 2016 shares
Capital structure
Limited partnership units owned	184,064,000	183,637,000	183,351,000	183,279,000
Redeemable noncontrolling interests in the Operating Partnership | $	$ 1,018,665	$ 972,740
Number of classes of LTIP Units | class	2
United Dominion Realty L.P.
Capital structure
Limited partnership units owned	176,200,000	174,200,000
Percentage of units	95.70%	94.90%
United Dominion Realty L.P.
Capital structure
General Partnership units outstanding	110,883	110,883
Limited partnership units owned	183,952,659	183,525,660
Required period to be outstanding before unit is redeemable (in years)	1 year
Redeemable noncontrolling interests in the Operating Partnership | $	$ 366,400	$ 371,900
UDR, Inc.
Capital structure
Limited partnership units owned	176,100,000	174,100,000
Percentage of units	95.70%	94.90%
UDR, Inc. | United Dominion Realty L.P.
Capital structure
General Partnership units outstanding	100,000	100,000
Limited partnership units owned	176,100,000	174,100,000
Percentage of units	95.70%	94.80%
Non-affiliated Partners
Capital structure
Limited partnership units owned	7,900,000
Percentage of units	4.30%	5.10%
Non-affiliated Partners | United Dominion Realty L.P.
Capital structure
Limited partnership units owned	7,900,000
Percentage of units	4.30%	5.10%
Class A Limited Partner
Capital structure
Cumulative, annual, non-compounded preferred return on Class A Partnership units	8.00%
Value of Class A Partnership units (in dollars per share) | $ / shares	$ 16.61
Class A Limited Partner | United Dominion Realty L.P.
Capital structure
Limited partnership units owned	1,900,000	1,900,000
Class A Limited Partner | UDR, Inc.
Capital structure
Limited partnership units owned	121,000	121,000	121,000	121,000
Non-affiliated Partners | United Dominion Realty L.P.
Capital structure
Limited partnership units owned	7,900,000	9,400,000
Percentage of units	4.30%	5.10%
Non-affiliated Partners | Class A Limited Partner
Capital structure
Limited partnership units owned	1,752,000	1,752,000	1,752,000	1,752,000
LTIP Units One
Capital structure
Vesting period	4 years
Minimum | LTIP Units
Capital structure
Vesting period	1 year
Period of time LTIP units have been outstanding	2 years
Minimum | Employee Director | LTIP Units
Capital structure
Vesting period	1 year
Maximum | LTIP Units
Capital structure
Vesting period	3 years
Maximum | Employee Director | LTIP Units
Capital structure
Vesting period	3 years