Commitments and Contingencies (Narrative) (Details)	6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($) partnership	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) partnership
DownREIT [Member]
Long-term Purchase Commitment [Line Items]
Number of real estate joint ventures | partnership	2		2
Shares issued in exchange of interests	$ 0	$ 100,000
Aggregate redemption value	60,000,000		$ 51,000,000
Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 52,200,000
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	$ 24,000,000
Future investment amount	$ 30,700,000