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Secured and Unsecured Debt (Details Textual 1) (USD $)
 3 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2012
1.67% Term Notes due December 2016 [Member]
Mar. 31, 2013
1.67% Term Notes due December 2016 [Member]
Mar. 31, 2012
1.67% Term Notes due December 2016 [Member]
Mar. 31, 2013
2.90% Term Notes due January 2016 [Member]
Mar. 31, 2012
2.90% Term Notes due January 2016 [Member]
Mar. 31, 2013
4.63% Medium-Term Notes due January 2022 [Member]
Dec. 31, 2012
4.63% Medium-Term Notes due January 2022 [Member]
Mar. 31, 2013
2.68% Term Notes due December 2016 [Member]
Dec. 31, 2012
2.68% Term Notes due December 2016 [Member]
Dec. 31, 2012
UDR Bank Credit Facility [Member]
Mar. 31, 2013
UDR Bank Credit Facility [Member]
Unsecured Debt (Textual) [Abstract]                            
Total revolving credit facility                         $ 900,000,000 $ 900,000,000
Initial term of credit facilities (in years) 10 years                       4 years  
Additional time period for extending facilities (in years)                         1 year  
Increase in maximum borrowing capacity of unsecured revolving credit facility                         1,350,000,000.00  
Credit facility interest rate   122.5                        
Line of Credit Facility, Commitment Fee Description   22.5                        
Fixed interest rate         1.64% 1.65% 2.90% 2.90% 4.63% 4.63% 2.68% 2.68%    
Interest rate                         1.40% 1.20%
Line of credit $ 2,500,000   $ 3,900,000                      
Debt Instrument, Maturity Date       Jan. 01, 2016