Debt (UNITED DOMINION REALTY, L.P.) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014 Communities	Dec. 31, 2013
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.94%
Weighted Average Years to Maturity		4 years 3 months 18 days
Fixed Rate Debt
Debt Instrument [Line Items]
Principal outstanding	$ 969,296	$ 969,296	$ 1,072,373
Weighted Average Interest Rate	5.26%
Weighted Average Years to Maturity		3 years 0 months 2 days
Number of Communities Encumbered		28
Fixed Rate Debt | Mortgage notes payable
Debt Instrument [Line Items]
Principal outstanding			445,706
Weighted Average Interest Rate	5.46%
Weighted Average Years to Maturity		1 year 7 months 20 days
Number of Communities Encumbered	6
Fixed Rate Debt | Fannie Mae credit facilities
Debt Instrument [Line Items]
Principal outstanding			626,667
Weighted Average Years to Maturity		4 years 0 months 10 days
Number of Communities Encumbered	22
Variable Rate Debt
Debt Instrument [Line Items]
Principal outstanding	392,233	392,233	369,704
Weighted Average Interest Rate	1.44%
Weighted Average Years to Maturity		5 years 8 months 7 days
Number of Communities Encumbered		10
Variable Rate Debt | Mortgage notes payable
Debt Instrument [Line Items]
Principal outstanding			63,595
Weighted Average Interest Rate	1.94%
Weighted Average Years to Maturity		2 years 0 months 25 days
Number of Communities Encumbered	1
Variable Rate Debt | Tax-exempt secured notes payable
Debt Instrument [Line Items]
Principal outstanding			94,700
Weighted Average Interest Rate	0.83%
Weighted Average Years to Maturity		8 years 2 months 8 days
Number of Communities Encumbered	2
Variable Rate Debt | Fannie Mae credit facilities
Debt Instrument [Line Items]
Principal outstanding			211,409
Weighted Average Years to Maturity		5 years 2 months 8 days
Number of Communities Encumbered	7
United Dominion Reality L.P.
Debt Instrument [Line Items]
Principal outstanding	931,959	931,959	934,865
Weighted Average Interest Rate		4.38%
Weighted Average Years to Maturity		4 years 0 months 7 days
Number of Communities Encumbered		21
United Dominion Reality L.P. | Fannie Mae credit facilities
Debt Instrument [Line Items]
Principal outstanding	526,600	526,600
United Dominion Reality L.P. | Fixed Rate Debt
Debt Instrument [Line Items]
Principal outstanding	712,199	712,199	765,806
Weighted Average Interest Rate		5.20%
Weighted Average Years to Maturity		3 years 0 months 2 days
Number of Communities Encumbered		15
United Dominion Reality L.P. | Fixed Rate Debt | Mortgage notes payable
Debt Instrument [Line Items]
Principal outstanding	378,371	378,371	386,803
Weighted Average Interest Rate		5.47%
Weighted Average Years to Maturity		1 year 7 months 2 days
Number of Communities Encumbered		5
United Dominion Reality L.P. | Fixed Rate Debt | Fannie Mae credit facilities
Debt Instrument [Line Items]
Weighted Average Interest Rate		4.90%
Weighted Average Years to Maturity		4 years 6 months 25 days
Number of Communities Encumbered		10
United Dominion Reality L.P. | Variable Rate Debt
Debt Instrument [Line Items]
Principal outstanding	219,760	219,760	169,059
Weighted Average Interest Rate		1.72%
Weighted Average Years to Maturity		7 years 4 months 15 days
Number of Communities Encumbered		6
United Dominion Reality L.P. | Variable Rate Debt | Mortgage notes payable
Debt Instrument [Line Items]
Weighted Average Years to Maturity		0 years
United Dominion Reality L.P. | Variable Rate Debt | Tax-exempt secured notes payable
Debt Instrument [Line Items]
Principal outstanding	$ 27,000	$ 27,000	$ 27,000
Weighted Average Interest Rate		0.93%
Weighted Average Years to Maturity		17 years 2 months 19 days
Number of Communities Encumbered		1
United Dominion Reality L.P. | Variable Rate Debt | Fannie Mae credit facilities
Debt Instrument [Line Items]
Weighted Average Interest Rate		1.83%
Weighted Average Years to Maturity		5 years 11 months 26 days
Number of Communities Encumbered		5