Reportable Segments (UNITED DOMINION REALTY, L.P.) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Segments	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	$ 188,613,000	$ 190,690,000	$ 372,914,000	$ 380,033,000
Reportable apartment home segment NOI	128,653,000	128,911,000	253,969,000	257,025,000
Reconciling items:
Property management	(5,187,000)	(5,244,000)	(10,255,000)	(10,451,000)
Other operating expenses	(1,807,000)	(1,434,000)	(3,450,000)	(2,817,000)
Depreciation and amortization	(85,131,000)	(84,474,000)	(168,573,000)	(178,721,000)
General and administrative	(9,866,000)	(13,738,000)	(19,342,000)	(23,117,000)
Hurricane-related (recoveries)/charges, net	2,772,000	0	5,793,000	0
Net gain on sale of depreciable property	0	172,006,000	0	252,531,000
Non-controlling interests	(3,000)	(43,000)	(7,000)	(95,000)
Net (loss)/income attributable to Entity	5,192,000	150,352,000	4,924,000	233,508,000
Reportable apartment home segment assets:
Total segment assets	8,016,688,000		8,016,688,000		8,055,828,000
Accumulated depreciation	(2,071,649,000)		(2,071,649,000)		(1,924,682,000)
Total real estate owned, net of accumulated depreciation	5,945,039,000		5,945,039,000		6,131,146,000
Reconciling items:
Cash and cash equivalents	9,035,000	184,112,000	9,035,000	184,112,000	12,115,000	12,503,000
Restricted cash	24,843,000		24,843,000		23,561,000
Deferred financing costs, net	27,043,000		27,043,000		24,990,000
Other assets	137,548,000		137,548,000		125,654,000
Total assets	6,743,543,000		6,743,543,000		6,859,103,000
Reportable Segment (Textual) [Abstract]
Number of reportable segments	2
Condition for Community considered to have stabilized occupancy			90% occupancy for at least three consecutive months
Percent occupancy to be considered a community			90.00%
Time to maintain percent occupancy to be considered a community			3 months
Number of Tenants or related group of tenants that contributed 10% or more of company total revenue	0	0	0	0
Reportable Segments Additional (Textual) [Abstract]
Capital expenditures related to segments	14,800,000	15,700,000	21,700,000	25,600,000
Same Store Communities Western Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	61,047,000	57,852,000	120,303,000	114,140,000
Reportable apartment home segment NOI	43,448,000	40,435,000	85,311,000	79,663,000
Reportable apartment home segment assets:
Total segment assets	2,412,380,000		2,412,380,000		2,422,987,000
Same Store Communities Mid-Atlantic Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	41,600,000	40,436,000	82,950,000	80,162,000
Reportable apartment home segment NOI	29,049,000	28,063,000	57,811,000	55,629,000
Reportable apartment home segment assets:
Total segment assets	1,424,669,000		1,424,669,000		1,419,873,000
Same Store Communities Northeast Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	14,564,000	13,450,000	28,663,000	26,593,000
Reportable apartment home segment NOI	10,699,000	9,725,000	20,770,000	19,026,000
Reportable apartment home segment assets:
Total segment assets	730,427,000		730,427,000		723,437,000
Same Store Communities Southeastern Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	28,934,000	27,364,000	57,478,000	54,376,000
Reportable apartment home segment NOI	18,812,000	17,764,000	37,516,000	35,356,000
Reportable apartment home segment assets:
Total segment assets	880,537,000		880,537,000		887,482,000
Same Store Communities Southwestern Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	11,162,000	10,472,000	22,168,000	20,639,000
Reportable apartment home segment NOI	6,966,000	6,019,000	13,667,000	12,190,000
Reportable apartment home segment assets:
Total segment assets	387,275,000		387,275,000		385,377,000
Non-Mature communities/Other [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	31,306,000	41,116,000	61,352,000	84,123,000
Reportable apartment home segment NOI	19,679,000	26,905,000	38,894,000	55,161,000
Reportable apartment home segment assets:
Total segment assets	2,181,400,000		2,181,400,000		2,216,672,000
Reportable Segments Additional (Textual) [Abstract]
Capital expenditures related to segments	1,323,502	1,600,000	1,645,962	4,000,000
United Dominion Reality L.P. [Member]
Segment Reporting Information [Line Items]
Related Party Transaction, Management Fee Percentage			2.75%
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	102,709,000	101,408,000	202,769,000	200,676,000
Reportable apartment home segment NOI	72,461,000	71,150,000	142,584,000	140,688,000
Reconciling items:
Property management	(2,824,000)	(2,789,000)	(5,576,000)	(5,519,000)
Other operating expenses	(1,423,000)	(1,305,000)	(2,809,000)	(2,623,000)
Depreciation and amortization	(45,307,000)	(46,733,000)	(90,700,000)	(98,410,000)
Interest	(9,050,000)	(12,891,000)	(18,312,000)	(25,861,000)
General and administrative	(5,894,000)	(7,295,000)	(11,469,000)	(14,946,000)
Hurricane-related (recoveries)/charges, net	2,257,000	0	4,276,000	0
Net gain on sale of depreciable property	0	51,266,000	0	51,182,000
Non-controlling interests	(66,000)	(231,000)	(112,000)	(265,000)
Net (loss)/income attributable to Entity	10,154,000	51,172,000	17,882,000	44,246,000
Reportable apartment home segment assets:
Total segment assets	4,262,645,000		4,262,645,000		4,182,920,000
Accumulated depreciation	(1,187,753,000)		(1,187,753,000)		(1,097,133,000)
Total real estate owned, net of accumulated depreciation	3,074,892,000		3,074,892,000		3,085,787,000
Reconciling items:
Cash and cash equivalents	3,197,000	1,174,000	3,197,000	1,174,000	2,804,000	704,000
Restricted cash	13,912,000		13,912,000		12,926,000
Deferred financing costs, net	6,516,000		6,516,000		6,072,000
Other assets	28,213,000		28,213,000		28,665,000
Total assets	3,126,730,000		3,126,730,000		3,136,254,000
Reportable Segment (Textual) [Abstract]
Number of reportable segments	2
Condition for Community considered to have stabilized occupancy	once it achieves 90% occupancy for at least three consecutive months
Number of Tenants or related group of tenants that contributed 10% or more of company total revenue	0	0	0	0
Reportable Segments Additional (Textual) [Abstract]
Capital expenditures related to segments	8,400,000	8,800,000	12,300,000	14,900,000
United Dominion Reality L.P. [Member] | Same Store Communities Western Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	46,848,000	44,442,000	92,179,000	87,665,000
Reportable apartment home segment NOI	33,596,000	31,369,000	65,840,000	61,677,000
Reportable apartment home segment assets:
Total segment assets	1,755,434,000		1,755,434,000		1,748,369,000
United Dominion Reality L.P. [Member] | Same Store Communities Mid-Atlantic Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	17,079,000	16,594,000	33,990,000	32,930,000
Reportable apartment home segment NOI	11,673,000	11,410,000	23,206,000	22,582,000
Reportable apartment home segment assets:
Total segment assets	703,932,000		703,932,000		701,741,000
United Dominion Reality L.P. [Member] | Same Store Communities Northeast Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	9,205,000	8,414,000	18,111,000	16,788,000
Reportable apartment home segment NOI	6,858,000	6,193,000	13,333,000	12,240,000
Reportable apartment home segment assets:
Total segment assets	438,113,000		438,113,000		434,138,000
United Dominion Reality L.P. [Member] | Same Store Communities Southeastern Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	10,750,000	10,078,000	21,336,000	20,063,000
Reportable apartment home segment NOI	6,936,000	6,592,000	13,941,000	13,169,000
Reportable apartment home segment assets:
Total segment assets	325,200,000		325,200,000		322,882,000
United Dominion Reality L.P. [Member] | Same Store Communities Southwestern Region [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	6,369,000	5,979,000	12,590,000	11,729,000
Reportable apartment home segment NOI	4,104,000	3,515,000	7,946,000	7,091,000
Reportable apartment home segment assets:
Total segment assets	225,282,000		225,282,000		224,429,000
United Dominion Reality L.P. [Member] | Non-Mature communities/Other [Member]
Summary of rental income and NOI for UDRs reportable segments and reconciliation of NOI to loss from continuing operations
Reportable apartment home segment rental income	12,458,000	15,901,000	24,563,000	31,501,000
Reportable apartment home segment NOI	9,294,000	12,071,000	18,318,000	23,929,000
Reportable apartment home segment assets:
Total segment assets	814,684,000		814,684,000		751,361,000
Reportable Segments Additional (Textual) [Abstract]
Capital expenditures related to segments	$ 249,000	$ 600,000	$ 328,000	$ 1,000,000