The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

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Real Estate Owned (Details Textual) $ / shares in Units, $ in Thousands	2 Months Ended	3 Months Ended								12 Months Ended
	Feb. 19, 2016 USD ($)	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) Communities	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 $ / shares	Dec. 31, 2015 Communities $ / shares	Dec. 31, 2015 $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2015 Apartment_Homes $ / shares	Dec. 31, 2015 $ / shares shares	Dec. 31, 2014 USD ($) Communities shares	Dec. 31, 2013 USD ($) Communities Apartment_Homes shares	Dec. 31, 2015 Communities	Dec. 31, 2015	Dec. 31, 2015 USD ($)	Dec. 31, 2015 Apartment_Homes	Dec. 31, 2015 ft²	Dec. 31, 2015 States
Real Estate Properties [Line Items]
Revenues													$ 894,638			$ 818,046	$ 758,926
Document Period End Date										Dec. 31, 2015
Real Estate Owned (Textual) [Abstract]
Number of apartment homes owned and consolidated by the Company \| Apartment_Homes																					40,728
Communities Sold											12	9
Apartment Homes Sold												2,500		2,735			914
Deferred Gain on Sale of Property						$ 24,700										24,700				$ 6,800
Joint venture, number of homes in communities \| Apartment_Homes																					6,696
Number of apartment homes acquired												358
Acquisition-related costs													2,100			400	$ 100
Number of Real Estate Properties																		133	2
Number of States in which Entity Operates																			10
Number of Communities Acquired												4
Other Cost and Expense, Operating													9,708			8,271	7,136
Proceeds from Sale of Property, Plant, and Equipment													408,700			328,400	81,100
Payments for (Proceeds from) Investments													(387,650)			(383,886)	(250,043)
Gain/(loss) on sales of real estate owned, net of tax													251,677			143,572	0
Gain (Loss) on Disposition of Property Plant Equipment													138,600
Noncash or Part Noncash Acquisition, Debt Assumed													0			0	63,595
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest		$ 4,528	$ 13,695	$ 10,842	$ 76,417	$ 6,485	$ 10,611	$ 4,359	$ (5,195)				$ 105,482			$ 16,260	2,340
Payments for Delayed Tax Exempt Exchange		221,000
CALIFORNIA
Real Estate Owned (Textual) [Abstract]
Number of Communities Acquired												2
Home Acquisition [Member]
Real Estate Owned (Textual) [Abstract]
Noncash or Part Noncash Acquisition, Debt Assumed		$ 89,300
Number of Properties Purchased		6
Business Combination, Consideration Transferred		$ 900,600
Business Acquisition, Share Price \| $ / shares		$ 35								$ 35	$ 35	$ 35	$ 35	$ 35	$ 35
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares \| shares		16,100,000
Cash Acquired from Acquisition		$ 25,500
Texas JV
Real Estate Owned (Textual) [Abstract]
Communities Sold												8
Deferred Gain on Sale of Property																				24,200
Proceeds from Sale of Property, Plant, and Equipment													$ 44,200
Gain (Loss) on Disposition of Property Plant Equipment													59,400
Operating Community [Member]
Real Estate Owned (Textual) [Abstract]
Communities Sold												1
Gain (Loss) on Disposition of Property Plant Equipment													142,500
Operating Community [Member] \| Unconsolidated Joint Venture Vitruvian Park [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent						50.00%										50.00%			50.00%
Number of Units in Real Estate Property																			1,130
Number of Real Estate Properties																			3
Operating Community [Member] \| Texas JV
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent						20.00%										20.00%			0.00%
Development Community [Member] \| Texas JV
Real Estate Owned (Textual) [Abstract]
Number of Units in Real Estate Property																			0
Number of Real Estate Properties																			0
Land
Real Estate Owned (Textual) [Abstract]
Gain (Loss) on Disposition of Property Plant Equipment													1,100
Lightbox [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions													45,500
Waterscape [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions													75,200
Graybar [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions																$ 32,200
Operating Community [Member]
Real Estate Owned (Textual) [Abstract]
Payments for (Proceeds from) Investments													(324,400)
Land
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions													77,800
13th & Market [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent																			49.00%
Proceeds from Sale of Property, Plant, and Equipment													54,200
Gain (Loss) on Disposition of Property Plant Equipment													7,200
3033 Wilshire
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent																			50.00%
Proceeds from Sale of Property, Plant, and Equipment													8,300
Gain (Loss) on Disposition of Property Plant Equipment													2,200
UDR Lighthouse DownREIT L.P. [Member]
Real Estate Properties [Line Items]
Revenues													15,600
Real Estate Owned (Textual) [Abstract]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest													9,200
1745 Shea [Member]
Real Estate Owned (Textual) [Abstract]
Noncash or Part Noncash Acquisition, Debt Assumed													24,067			0	0
Square Footage \| ft²																						120,000
1745 Shea [Member] \| Office Building [Member]
Real Estate Owned (Textual) [Abstract]
Property, Plant and Equipment, Additions													24,000
United Dominion Reality L.P.
Real Estate Properties [Line Items]
Revenues													440,408			$ 422,634	$ 410,842
Document Period End Date										Dec. 31, 2015
Real Estate Owned (Textual) [Abstract]
Number of apartment homes owned and consolidated by the Company \| Apartment_Homes																					16,974
Communities Sold												5				1	2
Apartment Homes Sold \| Apartment_Homes														1,149			914
Deferred Gain on Sale of Property						$ 24,622										$ 24,622				$ 0
Property, Plant and Equipment, Additions													142,000
Number of apartment homes acquired												421
Number of Real Estate Properties \| Communities																		57
Number of States in which Entity Operates \| States																							8
Other Cost and Expense, Operating													5,923			5,172	$ 5,728
Proceeds from Sale of Property, Plant, and Equipment													250,900			48,700	81,100
Payments for (Proceeds from) Investments													(232,400)			(47,900)
Gain/(loss) on sales of real estate owned, net of tax													158,123			63,635	0
Gain (Loss) on Disposition of Property Plant Equipment																$ 24,400
Communities Held For Sale \| Communities						0										0
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest		$ 14,516	$ 14,952	$ 15,355	$ 12,117	$ 9,939	$ 8,875	$ 8,319	$ 6,411				56,940			$ 33,544	$ 32,766
United Dominion Reality L.P. \| Home Acquisition [Member]
Real Estate Owned (Textual) [Abstract]
Number of Properties Purchased		1
United Dominion Reality L.P. \| Operating Community [Member]
Real Estate Owned (Textual) [Abstract]
Gain (Loss) on Disposition of Property Plant Equipment													62,500
United Dominion Reality L.P. \| Land
Real Estate Owned (Textual) [Abstract]
Gain (Loss) on Disposition of Property Plant Equipment													$ 1,100
Affiliated Entity [Member] \| Home Acquisition [Member]
Real Estate Owned (Textual) [Abstract]
Number of Properties Purchased		1
Subsequent Event [Member]
Real Estate Owned (Textual) [Abstract]
Proceeds from Sale of Property, Plant, and Equipment	$ 13,500
Payments for (Proceeds from) Investments	(9,600)
Gain (Loss) on Disposition of Property Plant Equipment	$ 2,100
UDR DownREIT Unit [Member] \| Home Acquisition [Member]
Real Estate Owned (Textual) [Abstract]
Stock Issued During Period, Value, Acquisitions		$ 564,800
Series F Preferred Stock [Member] \| Home Acquisition [Member]
Real Estate Owned (Textual) [Abstract]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares \| shares		13,988,313													270,628	801,054	533,966
UDR DownREIT Unit [Member]
Real Estate Owned (Textual) [Abstract]
Equity method investment, ownership percent																			50.10%