Commitments and Contingencies (UNITED DOMINION REALTY, L.P.) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Communities		Dec. 31, 2013	Dec. 31, 2012
Real Estate Properties [Line Items]
Costs Incurred to Date	$ 549,130,000
Expected Costs to Complete	255,747,000	[1]
Ground Leases
Real Estate Properties [Line Items]
Number of Real Estate Properties	6
2013	5,412,000	[2]
2014	5,412,000	[2]
2015	5,412,000	[2]
2016	5,412,000	[2]
2017	5,412,000	[2]
Thereafter	313,735,000	[2]
Rent expense	5,400,000		5,200,000	5,100,000
United Dominion Reality L.P.
Real Estate Properties [Line Items]
Capital Expenditures Incurred but Not yet Paid	7,254,000		6,371,000	7,440,000
Number of Real Estate Properties	68
United Dominion Reality L.P. | Ground Leases
Real Estate Properties [Line Items]
Number of Real Estate Properties	5
2013	5,300,000
2014	5,200,000
2015	5,200,000
2016	5,200,000
2017	5,200,000
Thereafter	313,600,000	[2]
Rent expense	5,300,000		5,100,000	5,000,000
Wholly-owned — under development
Real Estate Properties [Line Items]
Capital Expenditures Incurred but Not yet Paid	14,700,000
Number of Real Estate Properties	1
Costs Incurred to Date	177,632,000
Wholly-owned — redevelopment
Real Estate Properties [Line Items]
Capital Expenditures Incurred but Not yet Paid	1,800,000
Number of Real Estate Properties	1
Costs Incurred to Date	$ 83,778,000

[1] Represents 100% of project costs incurred to date.

[2] For purposes of our ground lease contracts, the Company uses the minimum lease payment, if stated in the agreement. For ground lease agreements where there is a reset provision based on the communities appraised value or consumer price index but does not include a specified minimum lease payment, the Company uses the current rent over the remainder of the lease term.