Archstone Acquisition (Details 2) (Archstone, USD $)	0 Months Ended			3 Months Ended			3 Months Ended		0 Months Ended
	Feb. 27, 2013 community	Feb. 27, 2013 Archstone Legacy Entities entity community	May 31, 2013 Archstone Legacy Entities	Mar. 31, 2013 Archstone U.S. Fund item community	Mar. 31, 2013 AC JV item home community	Feb. 27, 2013 AC JV	Mar. 31, 2013 Brandywine	Feb. 27, 2013 Brandywine item community	Feb. 27, 2013 Residual JV entity item home community
Investments in Archstone Legacy Entities
Indirect ownership interest (as a percent)		2758.00%
Number of operating communities in which Archstone Legacy Entities holds indirect interest		16
Number of operating communities acquired	60
Aggregate liquidation preference		$ 175,000,000
Liquidation preference subject to redemption at the election of the holders		102,000,000
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			66,500,000
Investments in Archstone Unconsolidated Entities
Equity interest held (as a percent)	40.00%					20.00%	28.70%	26.10%
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				218
Number of loans secured by individual assets				9	8
Debt outstanding				$ 329,684,000	$ 162,300,000		$ 17,665,000
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