Archstone Acquisition (Details 2) (Archstone, USD $)	0 Months Ended			6 Months Ended		6 Months Ended		6 Months Ended			0 Months Ended
	Feb. 27, 2013 community	Feb. 27, 2013 Archstone Legacy Entities entity community	Jun. 30, 2013 Archstone Legacy Entities	Jun. 30, 2013 Archstone U.S. Fund item community	Feb. 27, 2013 Archstone U.S. Fund	Jun. 30, 2013 AC JV item home community	Feb. 27, 2013 AC JV	Jun. 30, 2013 AC JV Maximum mi	Jun. 30, 2013 Brandywine item community	Feb. 27, 2013 Brandywine	Feb. 27, 2013 Residual JV item	Jun. 30, 2013 Residual JV item community
Investments in Archstone Consolidated Entities
Number of operating communities in which Archstone Legacy Entities holds indirect interest		16
Number of operating communities acquired	60
Aggregate liquidation preference			$ 90,000,000
Number of entities previously entered into tax protection arrangements		1
Percentage of the economic cost of preferred redemption obligations		40.00%
Economic cost of preferred redemption obligations fair value, proportionate share of entity			36,000,000
Investments in Archstone Unconsolidated Entities
Equity interest held (as a percent)	40.00%				28.60%		20.00%		28.70%	26.10%		20.00%
Number of communities owned				9		2						6
Number of apartment communities owned				1,728		818			305			1,902
Number of apartment homes in communities for development						444
Number of marina communities				1
Number of boat slips				229
Number of outstanding unsecured loans				8		8
Debt outstanding				$ 330,516,000		$ 162,300,000			$ 25,000,000
Number of existing assets within specified geographic radius considered for right of first offer						2
Maximum geographic radius for existing assets within considered for right of first offer								1
Number of members who hold various interests in the joint venture									5
Additional interest purchased									2.60%
Number of limited liability company agreements											3
Ownership interest held by subsidiaries of the entity (as a percent)												40.00%
Number of land parcels						2						2