Property Acquisitions, Discontinued Operations, And Assets Held For Sale (Narrative) (Details) (USD $)	1 Months Ended				3 Months Ended				6 Months Ended	12 Months Ended
	Jan. 31, 2013	Dec. 31, 2012	Jan. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2012 acre	Dec. 31, 2011	Dec. 31, 2010
Property Acquisitions, Discontinued Operations, And Assets Held For Sale [Abstract]
Acres of land acquired										22.6
Purchase price of land acquired										$ 33,600,000
Number of operating properties acquired										7
Number of apartment units in wholly owned property acquired		320	4,034							2,114
Purchase price of operating properties acquired										356,000,000
Percentage of voting interests acquired		50.00%	80.00%		50.00%				50.00%	50.00%
Number of unconsolidated equity method investments acquired		1	12
Cash consideration		15,900,000	99,500,000		15,900,000				15,900,000	15,900,000
Debt assumed		26,200,000	272,600,000		26,200,000				26,200,000	26,200,000
Gain on acquisition of controlling interest in joint ventures		17,200,000	40,200,000		17,227,000	40,191,000				57,418,000	0	0
Equity method investment ownership percentage				20.00%			20.00%				20.00%
Pro Forma Property Revenues of Acquiree since Acquisition Date, Actual										52,800,000
Pro Forma Property Expenses of Acquiree since Acquisition Date, Actual										21,000,000
Number of apartment units in property of which noncontrolling ownership interests were acquired										680
Number of fully consolidated joint ventures acquired										3
Purchase of non-controlling interests										16,482,000	0	0
Number of operating properties sold				2			4		2	11
Number of apartment homes in operating properties sold	770			788						3,213
Number of assets classified as held for sale		1			1				1	1
Impairment provision on technology investment								$ 1,000,000