UNAUDITED SUMMARIZED CONSOLIDATED QUARTERLY FINANCIAL DATA (UNITED DOMINION REALTY, L.P.) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Rental income	$ 302,745	$ 289,008	$ 278,463	$ 267,922	$ 264,732	$ 263,256	$ 256,634	$ 250,483	$ 1,138,138	$ 1,035,105	$ 984,309
Net income/(loss)									199,579	221,542	132,655
Income/(loss)	105,237	29,422	38,318	26,602	89,615	20,258	22,444	89,225	199,579	221,542	132,655
Net income/(loss) attributable to OP unitholders									184,965	203,106	121,558
United Dominion Realty L.P.
Quarterly Financial Data [Abstract]
Rental income	111,389	111,700	110,350	108,334	108,523	109,539	107,266	106,592	441,773	431,920	419,377
Income/(loss)	24,568	27,283	27,810	24,334	86,324	28,135	25,181	91,845	103,995	231,485	107,855
Net income/(loss) attributable to OP unitholders	$ 23,988	$ 26,835	$ 27,394	$ 23,946	$ 85,880	$ 27,695	$ 24,761	$ 91,427	$ 102,163	$ 229,763	$ 106,307
Income/(loss) attributable to OP unitholders per weighted average OP Unit - basic and diluted	$ 0.13	$ 0.15	$ 0.15	$ 0.13	$ 0.47	$ 0.15	$ 0.13	$ 0.50	$ 0.56	$ 1.25	$ 0.58