Acquisitions and Dispositions (Narrative) (Details) (USD $)	1 Months Ended				3 Months Ended		1 Months Ended
	Mar. 31, 2015	Jan. 31, 2015	Mar. 31, 2014 acre	Jan. 31, 2014 acre	Mar. 31, 2015	Mar. 31, 2014 acre	Apr. 30, 2015 acre
Area of Land			3.0	2.9		3.0
Payments to Acquire Land				$ 15,600,000
Business Acquisition, Percentage of Voting Interests Acquired	0.01%				0.01%
Number of fully consolidated joint ventures acquired					2
Number of apartment units in wholly owned property acquired					798
Purchase of non-controlling interests					9,500,000	0
Sales price of land parcels	400,000		6,300,000
Gain (loss) on disposition of land	100,000		400,000
Number of operating properties sold		2
Number of Apartment Units in operating Property Disposed		1,116
Proceeds from sale of operating properties		114,400,000
Gain (Loss) on Sale of Properties					85,100,000
Subsequent Event [Member]
Area of Land							50.0
Payments to Acquire Land							$ 36,300,000