UNCONSOLIDATED ENTITIES (UNITED DOMINION REALTY, L.P.) - Additional Information (Details) $ in Thousands	Jun. 30, 2019 USD ($) community item	Dec. 31, 2018 USD ($)
Unconsolidated entities
Number of real estate properties | community	135
Number of apartment homes owned and consolidated | item	42,292
Equity Method Investments | $	$ 769,000	$ 780,869
United Dominion Reality L.P.
Unconsolidated entities
Number of real estate properties | community	52
Number of apartment homes owned and consolidated | item	16,434
Equity Method Investments | $	$ 89,265	103,026
United Dominion Reality L.P. | UDR Lighthouse DownREIT L.P.
Unconsolidated entities
Number of real estate properties | community	12
Number of apartment homes owned and consolidated | item	5,657
Equity Method Investments | $	$ 89,300	$ 103,000