Subsequent Events/Other (Details) (USD $)	1 Months Ended	3 Months Ended		39 Months Ended
	May 08, 2013	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	May 09, 2013
Subsequent Event [Line Items]
Properties Acquired Subsequent	1
Number Of Consolidated Apartment Units Acquired	322
Land parcels acquired	1
Value Of Land Parcels and Rental Properties Acquired Subsequent	$ 108,000,000
Number of Apartment Properties Sold Subsequent	12
Number of Consolidated Apartment Units Sold Subsequent	3,924
Subsequent Event Sold Consolidated Property	552,800,000
Repayments of Notes Payable	400,000,000	0	253,858,000
Notional Amount of Interest Rate Derivatives					150,000,000
Proceeds from Issuance of Unsecured Debt	500,000,000
Proceeds from Debt, Net of Issuance Costs	495,600,000
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Maximum	3.998%
Payments for (Proceeds from) Hedge Investing Activities	44,700,000
Liquidation Value Preferred Interests					65,000,000.00
Business Combination, Acquisition Related Costs		100,000	500,000	86,000,000
Noncash Project Abandonment Costs		2,533,000	1,034,000
Other Nonoperating Expense		2,564,000	5,807,000
Settlement Expense			4,200,000
5.200% Notes [Member]
Subsequent Event [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.20%
Notional Amount of Interest Rate Derivatives					300,000,000
3.00% Notes [Member]
Subsequent Event [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					3.00%
Joint Venture Company Portion [Member]
Subsequent Event [Line Items]
Liquidation Value Preferred Interests					39,000,000.00
Archstone Transaction [Member]
Subsequent Event [Line Items]
Liquidation Value Preferred Interests		167,200,000.00		167,200,000.00
Business Acquisition, Percentage of Voting Interests Acquired		60.00%		60.00%	60.00%
Archstone [Member]
Subsequent Event [Line Items]
Other Nonoperating Expense			$ 1,500,000