Real Estate Disposition Activities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Real estate disposition activities
Proceeds from sale of real estate			$ 182,225,000	$ 22,371,000
Gain on sale of real estate	95,049,000	7,675,000	95,049,000	7,675,000
Summary of income from discontinued operations
Rental income	3,065,000	9,278,000	6,986,000	18,363,000
Operating and other expenses	(1,114,000)	(5,600,000)	(2,486,000)	(11,289,000)
Interest expense, net	(53,000)	(1,311,000)	(133,000)	(2,611,000)
Loss on extinguishment of debt	(602,000)		(602,000)
Depreciation expense	(144,000)	(2,084,000)	(895,000)	(4,160,000)
Income from discontinued operations	1,152,000	283,000	2,870,000	303,000
Waterford and Arlington Heights
Real estate disposition activities
Number of communities sold	2
Number of apartment homes sold	953
Proceeds from sale of real estate	173,750,000
Gain on sale of real estate	95,049,000
Unimproved land parcel in Chicago, IL
Real estate disposition activities
Proceeds from sale of land			12,300,000
Gain on sale of real estate			280,000
Number of unimproved land parcels sold			1
Impairment loss - land holdings			$ 16,363,000