Subsequent Events/Other (Details) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended		42 Months Ended
	Aug. 08, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Subsequent Event [Line Items]
Number of Apartment Properties Sold Subsequent	6
Number of Consolidated Apartment Units Sold Subsequent	2,033
Land parcels sold subsequent	1
Subsequent Event Sold Consolidated Property	$ 247,300,000
Notional Amount of Interest Rate Derivatives	150,000,000
Common Stock Capital Shares Reserved For Future Issuance Under Share Offering Program	13.0	17.0		17.0		17.0
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	13.0
Business Combination, Acquisition Related Costs				100,000	5,500,000	93,500,000
Noncash Project Abandonment Costs				3,365,000	3,565,000
Other Nonoperating Expense		981,000	8,802,000	3,544,000	14,603,000
Settlement Expense					4,200,000
Acquisition-related Costs [Member]
Subsequent Event [Line Items]
Other Nonoperating Expense					$ 9,100,000