UNCONSOLIDATED ENTITIES (UNITED DOMINION REALTY, L.P.) - Summary Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Total real estate, net	$ 8,348,249		$ 8,348,249			$ 8,470,748
Cash and cash equivalents	927	$ 1,895	927	$ 1,895		8,106		$ 185,216
Other assets	173,834		173,834			186,296
Total assets	9,551,388		9,551,388			9,636,472
Secured debt, net	933,087		933,087			1,149,441
Accounts payable, accrued expenses, and other liabilities	102,197		102,197			90,032
Total liabilities	5,457,950		5,457,950			5,228,493
Lease Revenue	308,845	289,008	934,920	835,393
Property operating expenses	(53,385)	(46,869)	(151,585)	(131,702)
Real estate depreciation and amortization	(151,949)	(127,391)	(462,481)	(357,793)
Operating income/(loss)	30,115	58,856	160,846	176,275
Interest expense	(62,268)	(42,523)	(140,182)	(110,482)
Other income/(loss)	(2,183)	(1,875)	(7,304)	(12,998)
Net income/(loss)	(27,217)	29,422	40,419	94,342
United Dominion Realty L.P.
Total real estate, net	2,010,597		2,010,597			2,078,592
Cash and cash equivalents	81	40	81	40		24		125
Other assets	26,909		26,909			24,241
Total assets	2,312,910		2,312,910			2,398,745
Secured debt, net	99,093		99,093			99,071
Accounts payable, accrued expenses, and other liabilities	13,182		13,182			12,226
Total liabilities	1,072,593		1,072,593			1,032,859
Total capital	1,240,317	1,400,217	1,240,317	1,400,217	$ 1,284,457	1,365,886	$ 1,429,738	$ 1,485,889
Lease Revenue	107,694	111,700	325,060	330,384
Property operating expenses	(18,389)	(17,835)	(51,623)	(50,945)
Real estate depreciation and amortization	(35,335)	(35,155)	(106,065)	(104,730)
Operating income/(loss)	27,886	37,187	90,443	108,591
Interest expense	(686)	(538)	(2,136)	(889)
Net income/(loss)	19,057	27,283	63,558	79,427
UDR Lighthouse DownREIT L.P. | United Dominion Realty L.P.
Total real estate, net	1,053,312		1,053,312			1,106,703
Cash and cash equivalents	23		23			20
Note receivable from the General Partner	308,020		308,020			222,853
Other assets	6,728		6,728			4,829
Total assets	1,368,083		1,368,083			1,334,405
Secured debt, net	506,539		506,539			427,592
Accounts payable, accrued expenses, and other liabilities	27,817		27,817			28,087
Total liabilities	534,356		534,356			455,679
Total capital	833,727		833,727			$ 878,726
Lease Revenue	33,182	32,434	97,967	96,065
Property operating expenses	(13,345)	(13,087)	(39,334)	(38,934)
Real estate depreciation and amortization	(21,229)	(20,620)	(63,326)	(61,424)
Operating income/(loss)	(1,392)	(1,273)	(4,693)	(4,293)
Interest expense	(4,179)	(4,162)	(11,405)	(11,979)
Other income/(loss)	(2,228)	(2,054)	(6,057)	(6,060)
Net income/(loss)	$ (3,343)	$ (3,381)	$ (10,041)	$ (10,212)