Discontinued Operations (UNITED DOMINION REALTY, L.P.) (Details) (USD $)	3 Months Ended								12 Months Ended			3 Months Ended		9 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012	Mar. 31, 2012	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment									$ 138,600,000
Discontinued Operations (Textual) [Abstract]
Number of communities sold									9
Number of apartment homes sold									2,500	914	6,507
Proceeds from Sale of Property, Plant, and Equipment									328,400,000	81,100,000	609,400,000
Summary of income from discontinued operations
Rental income									147,000	9,152,000	39,543,000
Rental expenses									225,000	3,511,000	14,106,000
Property management fee									4,000	252,000	1,087,000
Real estate depreciation									0	1,958,000	8,475,000
Interest									21,000	(62,000)	821,000
Income before net gain on the sale of property									(103,000)	3,493,000	15,054,000
Income/(loss) from discontinued operations	0	79,000	18,000	(87,000)	41,376,000	884,000	829,000	853,000	10,000	43,942,000	266,608,000
United Dominion Reality L.P.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment									24,400,000
Discontinued Operations (Textual) [Abstract]
Number of communities sold									1	2		4
Number of apartment homes sold										914			1,314
Proceeds from Sale of Property, Plant, and Equipment									48,700,000	81,100,000
Number of communities held for sale	0								0
Summary of income from discontinued operations
Rental income									0	8,989,000	15,745,000
Rental expenses									0	3,149,000	5,444,000
Property management fee									0	247,000	432,000
Real estate depreciation									0	1,935,000	3,320,000
Income before net gain on the sale of property									0	3,658,000	6,549,000
Net (loss)/gain on the sale of depreciable property									0	41,518,000	51,094,000
Income/(loss) from discontinued operations					42,407,000		882,000	905,000	0	45,176,000	57,643,000			982,000
Operating Community [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment									142,500,000
Discontinued Operations (Textual) [Abstract]
Number of communities sold									1
Operating Community [Member] | United Dominion Reality L.P.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment									62,500,000
Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment									1,100,000
Land | United Dominion Reality L.P.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment									$ 1,100,000