UNCONSOLIDATED ENTITIES (UNITED DOMINION REALTY, L.P.) - Summary Financial Information (Details) - UDR Lighthouse DownREIT L.P. - United Dominion Realty L.P. - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total real estate, net	$ 1,106,703	$ 1,167,720
Cash and cash equivalents	20	39
Note receivable from the General Partner	222,853	221,022
Other assets	4,829	5,561
Total assets	1,334,405	1,394,342
Secured debt, net	427,592	431,735
Other liabilities	28,087	26,597
Liabilities	455,679	458,332
Total capital	878,726	936,010
Total revenues	128,621	138,121	$ 134,669
Property operating expenses	(51,747)	(56,998)	(55,487)
Real estate depreciation and amortization	(82,283)	(85,872)	(84,000)
Gain/(loss) on sale of real estate		24,053
Operating income/(loss)	(5,409)	19,304	(4,818)
Interest expense	(15,648)	(14,456)	(14,483)
Other income/(loss)	8,061	4,884	4,718
Net income /(loss)	$ (12,996)	$ 9,732	$ (14,583)