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Unconsolidated Entities (UNITED DOMINION REALTY, L.P.) Unconsolidated Entities (UNITED DOMINION REALTY, L.P.) (Details)
$ in Thousands
Dec. 31, 2015
Communities
Dec. 31, 2015
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Schedule of Equity Method Investments [Line Items]        
Number of Real Estate Properties 133 2    
Investment in unconsolidated entities     $ 938,906 $ 718,226
United Dominion Reality L.P.        
Schedule of Equity Method Investments [Line Items]        
Number of Real Estate Properties | Communities 57      
Investment in unconsolidated entities     $ 166,186 0
United Dominion Reality L.P. | UDR Lighthouse DownREIT L.P. [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of Real Estate Properties   13    
Number of Units in Real Estate Property   6,261    
Investment in unconsolidated entities       $ 0
Equity Method Investment, Ownership Percentage   41.60%   0.00%