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JOINT VENTURES AND PARTNERSHIPS - Summary (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) community item	Sep. 30, 2017 USD ($) item	Sep. 30, 2018 USD ($) community item	Sep. 30, 2017 USD ($) item	Aug. 31, 2018 item	Dec. 31, 2017 USD ($)	May 31, 2017	Mar. 31, 2017	Jan. 31, 2017	May 31, 2015 community
Financial information relating to unconsolidated joint ventures operations
Operating income/(loss)	$ (1,382)	$ 1,819	$ (5,091)	$ 11,591
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	767,376		767,376			$ 720,830
Deferred gains on the sale of depreciable property	$ 11,100		$ 11,100			10,900
Number of real estate properties \| community	127		127
Investment in and advances to unconsolidated joint ventures, net	$ 767,376		$ 767,376			720,830
Unconsolidated Joint Ventures
Financial information relating to unconsolidated joint ventures operations
Total revenues	76,203	71,200	215,140	205,475
Property operating expenses	30,096	28,157	85,435	79,622
real estate depreciation and amortization	29,545	28,264	85,063	82,344
Operating income/(loss)	16,562	14,779	44,642	43,509
Interest expense	(22,919)	(21,849)	(63,990)	(64,083)
Gain (loss) on sale of property		30,153		30,153
Other income/(loss)	40	(515)	141	(435)
Net income /(loss)	(6,317)	$ 22,568	(19,207)	$ 9,144
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	3,267,944		3,267,944			3,236,180
Cash and cash equivalents	53,141		53,141			36,411
Other assets	91,246		91,246			50,158
Total assets	3,412,331		3,412,331			3,322,749
Third party debt	2,108,790		2,108,790			2,005,566
Accounts payable and accrued liabilities	63,220		63,220			85,643
Total liabilities	2,172,010		2,172,010			2,091,209
Total equity	1,240,321		1,240,321			1,231,540
Investment in unconsolidated entities	569,038		569,038			599,196
Unconsolidated Joint Venture West Coast Development JV
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 102,100		$ 102,100			102,100
Preferred Equity Investment West Coast Development JV
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR's Ownership Interest	49.00%		49.00%				49.00%	49.00%	49.00%	48.00%
Number of real estate properties \| community										5
Rate	6.50%		6.50%
Preferred Equity Investment 1200 Broadway Nashville TN
Combined summary of balance sheets relating to unconsolidated joint ventures
Number of apartment homes \| item		313		313
Rate		8.00%		8.00%
Preferred Equity Investment 1641 Lincoln Santa Monica CA
Combined summary of balance sheets relating to unconsolidated joint ventures
Number of apartment homes \| item					66
Rate					12.00%
Preferred Equity Investment 1300 Fairmount Philadelphia, PA
Combined summary of balance sheets relating to unconsolidated joint ventures
Number of apartment homes \| item					471
Rate					9.00%
Preferred Equity Investment Essex Orlando, FL
Combined summary of balance sheets relating to unconsolidated joint ventures
Number of apartment homes \| item	330		330
Rate	12.50%		12.50%
Development Community
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 198,338		$ 198,338			121,634
Development Community \| Unconsolidated Joint Venture UDR Met Life I Partnership
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 34,869		$ 34,869			$ 34,653
UDR's Ownership Interest	50.00%		50.00%			50.00%
Number of apartment homes \| community	150		150
Number of real estate properties \| community	1		1
Development Community \| Unconsolidated Joint Venture Vitruvian Park
Combined summary of balance sheets relating to unconsolidated joint ventures
Number of real estate properties \| community	1		1
Development Community \| Preferred Equity Investment West Coast Development JV
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 65,476		$ 65,476			$ 64,226
Income from investments	$ 25	$ 3,266	$ 974	$ 16,626
Rate	6.50%		6.50%
Development Community \| Preferred Equity Investment 1532 Harrison San Francisco, CA
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 24,645		$ 24,645
Investment in unconsolidated entities	21,373		21,373			11,346
Income from investments	$ 721	226	$ 1,492	228
Rate	11.00%		11.00%
Years to Maturity			3 years 9 months 18 days
Development Community \| Preferred Equity Investment 1200 Broadway Nashville TN
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 55,558		$ 55,558
Investment in unconsolidated entities	48,805		48,805			18,011
Income from investments	$ 859	65	$ 1,870	65
Rate	8.00%		8.00%
Years to Maturity			4 years
Development Community \| Preferred Equity Investment 1641 Lincoln Santa Monica CA
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 8,800		$ 8,800
Investment in unconsolidated entities	8,938		8,938
Income from investments	$ 141		$ 141
Rate	12.00%		12.00%
Years to Maturity			4 years
Development Community \| Preferred Equity Investment 1300 Fairmount Philadelphia, PA
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 51,393		$ 51,393
Investment in unconsolidated entities	2,670		2,670
Income from investments	$ 27		$ 27
Rate	9.00%		9.00%
Years to Maturity			5 years
Development Community \| Preferred Equity Investment Essex Orlando, FL
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 12,886		$ 12,886
Investment in unconsolidated entities	6,326		6,326
Income from investments	$ 46		$ 46
Rate	12.50%		12.50%
Years to Maturity			5 years
Development Community \| Other Investment The Portals Washington, DC
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 38,559		$ 38,559
Investment in unconsolidated entities	41,996		41,996			26,535
Income from investments	$ 1,015	$ 330	$ 2,523	$ 346
Rate	11.00%		11.00%
Years to Maturity			2 years 8 months 12 days
Development Community \| Other Investment Ventures
Combined summary of balance sheets relating to unconsolidated joint ventures
UDR commitment	$ 15,000		$ 15,000
Investment in unconsolidated entities	2,754		2,754			1,516
Income from investments	(77)		(262)
Operating Community \| Unconsolidated Joint Venture UDR MetLife II Partnership
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 299,953		$ 299,953			$ 303,702
UDR's Ownership Interest	50.00%		50.00%			50.00%
Number of apartment homes \| community	4,059		4,059
Number of real estate properties \| community	18		18
Operating Community \| Unconsolidated Joint Venture Other MetLife
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 119,893		$ 119,893			$ 135,563
UDR's Ownership Interest	50.60%		50.60%			50.60%
Number of apartment homes \| community	1,437		1,437
Number of real estate properties \| community	5		5
Operating Community \| Unconsolidated Joint Venture Vitruvian Park
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 71,225		$ 71,225			$ 78,404
UDR's Ownership Interest	50.00%		50.00%			50.00%
Number of apartment homes \| community	1,513		1,513
Number of real estate properties \| community	3		3
Operating Community \| Unconsolidated Joint Venture Three Washington DC
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 6,453		$ 6,453			$ 8,958
UDR's Ownership Interest	30.00%		30.00%			30.00%
Number of apartment homes \| community	660		660
Number of real estate properties \| community	3		3
Operating Community \| Unconsolidated Joint Venture West Coast Development JV
Combined summary of balance sheets relating to unconsolidated joint ventures
Investment in unconsolidated entities	$ 36,645		$ 36,645			$ 37,916
UDR's Ownership Interest	47.00%		47.00%			47.00%
Number of apartment homes \| community	293		293
Number of real estate properties \| community	1		1
Land Parcel \| Unconsolidated Joint Venture Vitruvian Park
Combined summary of balance sheets relating to unconsolidated joint ventures
Number of real estate properties \| community	5		5