Real Estate Owned (UNITED DOMINION REALTY, L.P.) (Details Textual) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended
	Sep. 30, 2014	Dec. 31, 2014 Communities Apartment_Homes	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012
Real Estate Properties [Line Items]
Number of States in which Entity Operates		10
Real Estate Owned (Textual) [Abstract]
Number of apartments owned		39,851
Number of communities acquired apartment homes are within		0
Number of apartment homes acquired	358
Development costs excluding direct costs and capitalized interest		$ 8,953,000	$ 11,100,000	$ 10,000,000
Capitalized Interest Costs, Including Allowance for Funds Used During Construction		20,200,000	29,400,000	26,400,000
Other Cost and Expense, Operating		8,271,000	7,136,000	5,718,000
Communities Sold		9
Proceeds from Sale of Property, Plant, and Equipment		328,400,000	81,100,000	609,400,000
Gain (Loss) on Disposition of Property Plant Equipment		138,600,000
Payments for (Proceeds from) Investments		(383,886,000)	(250,043,000)	(593,167,000)
Gain/(loss) on sales of real estate owned		143,572,000	0	0
United Dominion Reality L.P.
Real Estate Properties [Line Items]
Number of States in which Entity Operates		9
Real Estate Owned (Textual) [Abstract]
Number of apartments owned		20,814
Development costs excluding direct costs and capitalized interest		2,010,000	2,500,000	2,100,000
Capitalized Interest Costs, Including Allowance for Funds Used During Construction		2,900,000	5,900,000	3,700,000
Other Cost and Expense, Operating		5,172,000	5,728,000	5,272,000
Communities Sold		1	2		4
Proceeds from Sale of Property, Plant, and Equipment		48,700,000	81,100,000
Gain (Loss) on Disposition of Property Plant Equipment		24,400,000
Payments for (Proceeds from) Investments		(47,922,000)
Gain/(loss) on sales of real estate owned		63,635,000	0	0
New York Properties [Member]
Real Estate Owned (Textual) [Abstract]
Number of Communities Owned				3	3
Number of Apartments Owned				1,706	1,706
Impairment of Long-Lived Assets Held-for-use			0	9,000,000
Other Cost and Expense, Operating				10,400,000
New York Properties [Member] | United Dominion Reality L.P.
Real Estate Owned (Textual) [Abstract]
Number of Communities Owned				2	2
Number of Apartments Owned				1,001	1,001
Hurricane Sandy [Member]
Real Estate Owned (Textual) [Abstract]
Total Estimated Insurance Recovery				14,500,000
Hurricane Sandy [Member] | United Dominion Reality L.P.
Real Estate Owned (Textual) [Abstract]
Impairment of Long-Lived Assets Held-for-use			0	7,100,000
Other Cost and Expense, Operating				7,000,000
Total Estimated Insurance Recovery			10,800,000	10,800,000
Unconsolidated Joint Venture Four Texas [Member] | United Dominion Reality L.P.
Real Estate Owned (Textual) [Abstract]
Communities Sold		2
Gain (Loss) on Disposition of Property Plant Equipment		$ 39,200,000