Commitments And Contingencies (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015 partnerships	Mar. 31, 2014	Dec. 31, 2014 partnerships
Long-term Purchase Commitment [Line Items]
Shares issued in exchange of interests		$ 0
DownREIT [Member]
Long-term Purchase Commitment [Line Items]
Number of real estate joint ventures	3		3
Shares issued in exchange of interests	100,000	0
Aggregate redemption value	53,000,000		52,000,000
Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	65,100,000
Capital Additions [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Construction contract, period (in months)	12 months
Capital Additions [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Construction contract, period (in months)	36 months
Development Addition [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment			23,800,000
Future investment amount			$ 29,100,000