Secured and Unsecured Debt (Details Textual) (USD $)	3 Months Ended	6 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended					12 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Fixed Rate Debt [Member]	Dec. 31, 2012 Fixed Rate Debt [Member]	Jun. 30, 2013 Variable Rate Debt [Member]	Dec. 31, 2012 Variable Rate Debt [Member]	Jun. 30, 2013 Mortgages Notes Payable [Member] Fixed Rate Debt [Member]	Jun. 30, 2013 Mortgages Notes Payable [Member] Fixed Rate Debt [Member]	Dec. 31, 2012 Mortgages Notes Payable [Member] Fixed Rate Debt [Member]	Jun. 30, 2013 Mortgages Notes Payable [Member] Variable Rate Debt [Member]	Dec. 31, 2012 Mortgages Notes Payable [Member] Variable Rate Debt [Member]	Jun. 30, 2013 Debt Assumed As Part of Acquisition [Member]	Jun. 30, 2012 Debt Assumed As Part of Acquisition [Member]	Jun. 30, 2013 Debt Assumed As Part of Acquisition [Member]	Jun. 30, 2012 Debt Assumed As Part of Acquisition [Member]	Jun. 30, 2013 Tax Exempt Notes Payable [Member] Variable Rate Debt [Member]	Dec. 31, 2012 Tax Exempt Notes Payable [Member] Variable Rate Debt [Member]	Jun. 30, 2013 Fannie Mae credit facilities [Member] Fixed Rate Debt [Member] credit_facility	Dec. 31, 2012 Fannie Mae credit facilities [Member] Fixed Rate Debt [Member]	Jun. 30, 2013 Fannie Mae credit facilities [Member] Variable Rate Debt [Member]	Dec. 31, 2012 Fannie Mae credit facilities [Member] Variable Rate Debt [Member]	Jun. 30, 2013 Tax Exempt Secured Notes Payable [Member] Variable Rate Debt [Member]	Jun. 30, 2013 Tax Exempt Secured Notes Payable [Member] Variable Rate Debt [Member]	Jun. 30, 2013 UDR Bank Credit Facility [Member]	Dec. 31, 2012 UDR Bank Credit Facility [Member]	Jun. 30, 2013 Line of Credit [Member] Carrying (Reported) Amount, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Fannie Mae credit facilities [Member] Variable Rate Debt [Member]	Jun. 30, 2013 Mortgages Notes Payable [Member] Carrying (Reported) Amount, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Fannie Mae credit facilities [Member] Fixed Rate Debt [Member]	Dec. 31, 2012 End of range of inital term of debt [Member] Fannie Mae credit facilities [Member]
Secured Debt (Textual) [Abstract]
Secured debt amount which encumbers real estate owned based upon book value	$ 2,200,000,000	$ 2,200,000,000
Percentage of secured debt which encumbers real estate owned based upon book value	27.10%	27.10%
Secured debt amount of real estate owned which is unencumbered	5,800,000,000	5,800,000,000
Percentage of secured debt of real estate owned which is unencumbered	72.90%	72.90%
Number of secured credit facilities																			3
Credit facilities with aggregate commitment																			928,500,000						900,000,000	900,000,000
Secured debt including debt on real estate held for sale				1,078,925,000	1,086,611,000	306,109,000	343,524,000	450,641,000	450,641,000	455,533,000	0	37,415,000					94,700,000	94,700,000		631,078,000	211,409,000	211,409,000					211,409,000	628,284,000
Initial term of credit facilities (in years)	10 years	10 years																											10 years
Weighted average interest rate	4.20%			5.17%		1.40%		5.42%			0.00%						0.89%
Unamortized fair market adjustment	14,400,000	14,400,000	16,900,000
Debt Instrument, Maturity Date Range, Start									Dec. 01, 2014										May 01, 2017				Aug. 01, 2019
Debt instrument, maturity date range, end									May 01, 2019										Jul. 01, 2023				Mar. 20, 2032
Notes payable minimum interest rates range									3.43%															0.82%
Notes payable maximum interest rates range									5.94%															1.05%
Amortization of Debt Discount (Premium)													$ 1,200,000	$ 1,200,000	$ 2,500,000	$ 2,300,000