Income/(Loss) Per Share (UNITED DOMINION REALTY, L.P.) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 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	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest													$ (5,511)	$ 48	$ 2,089
Income (Loss) from Continuing Operations Attributable to Parent													154,324	2,448	(44,356)
Income/(loss) from discontinued operations	0		79		18		(87)		41,376	884	829	853	10	43,942	266,608
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest													159,842	46,282	220,303
Comprehensive (Income) Loss, Net of Tax, Attributable to Noncontrolling Interest													5,375	1,720	8,206
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest													0	(1,578)	(10,075)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent													10	42,364	256,533
United Dominion Reality L.P.
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations Attributable to Parent													96,227	28,652	(13,409)
Income/(loss) from discontinued operations									42,407		882	905	0	45,176	57,643	982
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest													97,179	77,942	44,334
Comprehensive (Income) Loss, Net of Tax, Attributable to Noncontrolling Interest													952	4,566	352
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted													183,279	184,196	184,281
Income (Loss) from Continuing Operations, Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax													$ 0.53	$ 0.16	$ (0.07)
Income (Loss) from Discontinued Operations, Net of Tax, Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted													$ 0.00	$ 0.24	$ 0.31
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.18	[1]	$ 0.05	[1]	$ 0.13	[1]	$ 0.17	[1]	$ 0.24		$ 0.06	$ 0.04	$ 0.53	$ 0.40	$ 0.24	$ 0.06
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest													0	(452)	(252)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent													0	44,724	57,391
Noncontrolling Interest
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest													3	60	(140)
Noncontrolling Interest | United Dominion Reality L.P.
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest													$ (952)	$ (4,114)	$ (100)

[1] Quarterly income/(loss) per OP Unit amounts may not total to the annual amounts