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JOINT VENTURES AND PARTNERSHIPS - Summary (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) property community home	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) property community home	Sep. 30, 2019 USD ($)	Jul. 31, 2020 USD ($) home	Jun. 30, 2020 USD ($)	Feb. 29, 2020 USD ($) home	Jan. 31, 2020 home	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Unconsolidated entities
Investment in unconsolidated entities	$ 641,858		$ 641,858						$ 585,490
Number of real estate properties \| community	148		148
Combined summary of balance sheets relating to unconsolidated joint ventures
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
Accounts payable, accrued expenses, and other liabilities	102,197		102,197						90,032
Total liabilities	5,457,950		5,457,950						5,228,493
Total equity	3,333,452	3,271,775	3,333,452	3,271,775		$ 3,414,945			3,389,314	$ 2,968,015	$ 2,922,777
Financial information relating to unconsolidated joint ventures operations
Reportable apartment home segment rental income	310,044	295,394	938,781	847,375
Property operating and maintenance	53,385	46,869	151,585	131,702
Real estate depreciation and amortization	151,949	127,391	462,481	357,793
Operating income	30,115	58,856	160,846	176,275
Total amount of Interest expense presented on the Consolidated Statements of Operations	(62,268)	(42,523)	(140,182)	(110,482)
Gain/(loss) on sale of real estate owned			61,303	5,282
Other income/(loss)	2,183	1,875	7,304	12,998
Net income/(loss)	(27,217)	29,422	40,419	94,342
Unconsolidated Joint Ventures
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	1,947,336		1,947,336						1,901,081
Cash and cash equivalents	30,924		30,924						29,823
Other Assets	226,578		226,578						172,941
Total assets	2,204,838		2,204,838						2,103,845
Third party debt, net	1,194,684		1,194,684						1,148,048
Accounts payable, accrued expenses, and other liabilities	49,352		49,352						55,114
Total liabilities	1,244,036		1,244,036						1,203,162
Total equity	960,802		960,802						$ 900,683
Financial information relating to unconsolidated joint ventures operations
Reportable apartment home segment rental income	36,335	75,378	114,961	233,836
Property operating and maintenance	16,697	27,505	46,462	87,073
Real estate depreciation and amortization	16,929	26,027	50,085	83,661
Operating income	2,709	21,846	18,414	63,102
Total amount of Interest expense presented on the Consolidated Statements of Operations	(9,955)	(20,779)	(30,451)	(64,309)
Gain/(loss) on sale of real estate owned		97,201		115,558
Net unrealized gain/(loss) on held investments	(17)	25,669	29,295	27,191
Other income/(loss)	18	82	127	194
Net income/(loss)	(7,245)	124,019	17,385	141,736
Preferred Equity Investment Hillsboro Oregon
Unconsolidated entities
Number of apartment homes \| home								276
UDR's Ownership Interest								100.00%	49.00%
Preferred Equity Investment Thousand Oaks
Unconsolidated entities
Number of apartment homes \| home							142
Rate							9.00%
Preferred Equity Investment Thousand Oaks \| Maximum
Unconsolidated entities
UDR commitment							$ 20,100
Preferred Equity Investment Queens, New York
Unconsolidated entities
Number of apartment homes \| home					534
UDR commitment					$ 40,000
Rate					13.00%
Operating Community
Unconsolidated entities
Investment in unconsolidated entities	296,374		296,374						$ 313,053
Income from investments	$ (4,491)	3,332	$ (9,944)	1,498
Operating Community \| Unconsolidated Joint Venture UDR Met Life I Partnership
Unconsolidated entities
Number of apartment homes \| home	150		150
Investment in unconsolidated entities	$ 27,192		$ 27,192						$ 28,812
UDR's Ownership Interest	50.00%		50.00%						50.00%
Number of real estate properties \| property	1		1
Income from investments	$ (751)	(500)	$ (1,863)	(1,625)
Operating Community \| Unconsolidated Joint Venture UDR MetLife II Partnership
Unconsolidated entities
Number of apartment homes \| home	1,250		1,250
Investment in unconsolidated entities	$ 149,237		$ 149,237						$ 150,893
UDR's Ownership Interest	50.00%		50.00%						50.00%
Number of real estate properties \| property	7		7
Income from investments	$ (441)	702	$ (522)	1,912
Operating Community \| Unconsolidated Joint Venture Other MetLife
Unconsolidated entities
Number of apartment homes \| home	1,437		1,437
Investment in unconsolidated entities	$ 85,662		$ 85,662						$ 98,441
UDR's Ownership Interest	50.60%		50.60%						50.60%
Number of real estate properties \| property	5		5
Income from investments	$ (3,151)	(1,205)	$ (7,275)	(4,666)
Operating Community \| Unconsolidated Joint Venture West Coast Development JV
Unconsolidated entities
Number of apartment homes \| home	293		293
Investment in unconsolidated entities	$ 34,283		$ 34,283						$ 34,907
UDR's Ownership Interest	47.00%		47.00%						47.00%
Number of real estate properties \| property	1		1
Income from investments	$ (148)	(229)	$ (284)	(736)
Operating Community \| Sold Joint Ventures
Unconsolidated entities
Income from investments		4,564		6,613
Development Community \| Preferred Equity Investment Hillsboro Oregon
Unconsolidated entities
Investment in unconsolidated entities									$ 17,064
Rate	6.50%		6.50%
Income from investments		(237)	$ (46)	(409)
Development Community \| Preferred Equity Investment 1532 Harrison San Francisco, CA
Unconsolidated entities
Investment in unconsolidated entities	$ 33,162		33,162						30,585
UDR commitment	$ 24,645		$ 24,645
Rate	11.00%		11.00%
Years to Maturity			1 year 8 months 12 days
Income from investments	$ 875	802	$ 2,557	2,324
Participating Loan Years to Maturity			1 year 8 months 12 days
Development Community \| Preferred Equity Investment 1200 Broadway Nashville TN
Unconsolidated entities
Investment in unconsolidated entities	67,940		$ 67,940						63,958
UDR commitment	$ 55,558		$ 55,558
Rate	8.00%		8.00%
Years to Maturity			2 years
Income from investments	$ 1,347	1,244	$ 3,934	3,619
Participating Loan Years to Maturity			2 years
Development Community \| Preferred Equity Investment 1641 Lincoln Santa Monica CA
Unconsolidated entities
Investment in unconsolidated entities	11,353		$ 11,353						10,379
UDR commitment	$ 8,800		$ 8,800
Rate	12.00%		12.00%
Years to Maturity			1 year 9 months 18 days
Income from investments	$ 337	299	$ 974	861
Participating Loan Years to Maturity			1 year 9 months 18 days
Development Community \| Preferred Equity Investment 1300 Fairmount Philadelphia, PA
Unconsolidated entities
Investment in unconsolidated entities	58,286		$ 58,286						51,215
UDR commitment	51,393		$ 51,393
Years to Maturity			2 years 9 months 18 days
Income from investments	1,230	930	$ 3,587	1,724
Participating Loan Years to Maturity			2 years 9 months 18 days
Development Community \| Preferred Equity Investment Essex Orlando, FL
Unconsolidated entities
Investment in unconsolidated entities	16,253		$ 16,253						14,804
UDR commitment	$ 12,886		$ 12,886
Rate	12.50%		12.50%
Years to Maturity			2 years 10 months 24 days
Income from investments	$ 501	443	$ 1,448	1,182
Participating Loan Years to Maturity			2 years 10 months 24 days
Development Community \| Preferred Equity Investment Modera Lake Merritt, Oakland
Unconsolidated entities
Investment in unconsolidated entities	30,238		$ 30,238						22,653
UDR commitment	$ 27,250		$ 27,250
Rate	9.00%		9.00%
Years to Maturity			3 years 6 months
Income from investments	$ 675	366	$ 1,901	622
Participating Loan Years to Maturity			3 years 6 months
Development Community \| Preferred Equity Investment Thousand Oaks, CA
Unconsolidated entities
Investment in unconsolidated entities	13,693		$ 13,693
UDR commitment	$ 20,059		$ 20,059
Rate	9.00%		9.00%
Years to Maturity			4 years 3 months 18 days
Income from investments	$ 240		$ 417
Participating Loan Years to Maturity			4 years 3 months 18 days
Development Community \| Preferred Equity Investment Queens, New York
Unconsolidated entities
Investment in unconsolidated entities	41,002		$ 41,002
UDR commitment	$ 40,000		$ 40,000
Rate	13.00%		13.00%
Years to Maturity			4 years 9 months 18 days
Income from investments	$ 990		$ 990
Participating Loan Years to Maturity			4 years 9 months 18 days
Development Community \| Other Investment The Portals Washington, DC
Unconsolidated entities
Investment in unconsolidated entities	52,162		$ 52,162						48,181
UDR commitment	$ 38,559		$ 38,559
Rate	11.00%		11.00%
Years to Maturity			8 months 12 days
Income from investments	$ 1,448	1,287	$ 4,172	3,694
Participating Loan Years to Maturity			8 months 12 days
Development Community \| Other Investment Ventures
Unconsolidated entities
Investment in unconsolidated entities	21,395		$ 21,395						13,598
UDR commitment	34,500		34,500
Income from investments	(212)	4,247	4,338	4,272
Development Community \| Preferred Equity Investments and Other Investments
Unconsolidated entities
Investment in unconsolidated entities	345,484		345,484						$ 272,437
Income from investments	$ 7,431	$ 9,381	$ 24,272	$ 17,889