Commitments and Contingencies (Narrative) (Details)	6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) partnerships	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) partnership
Long-term Purchase Commitment [Line Items]
Acquisition of noncontrolling interests		$ 0
DownREIT [Member]
Long-term Purchase Commitment [Line Items]
Number of real estate joint ventures	3		3
Acquisition of noncontrolling interests	$ 100,000	$ 0
Aggregate redemption value	48,000,000		$ 52,000,000
Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 58,800,000
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			$ 29,200,000