Consolidation and Basis of Presentation (UNITED DOMINION REALTY, L.P.) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Markets Apartment_Homes Communities	Jun. 30, 2012	Jun. 30, 2013 Markets Apartment_Homes Communities	Jun. 30, 2012	Dec. 31, 2012
Entity Information [Line Items]
Number of communities owned (in communities)	141		141
Number of apartments owned (in apartments homes)	41,153		41,153
Operating Partnership outstanding units	184,281,253		184,281,253
OP units outstanding related to general partner	174,957,876		174,957,876
Percentage of units owned by UDR	94.90%		94.90%
United Dominion Reality L.P. [Member]
Entity Information [Line Items]
Rental revenues percent of General Partner's consolidated rental revenues	54.00%	53.00%	54.00%	53.00%
Number of communities owned (in communities)	70		70
Number of markets operating within (in markets)	18		18
Number of apartments owned (in apartments homes)	21,660		21,660
OP units outstanding related to general partner	110,883		110,883		110,883
OP units outstanding related to limited partner	184,170,370		184,170,370		184,170,370