Investments in Real Estate Entities (Details 2) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Assets:
Real estate, net	$ 1,854,887,000		$ 1,854,887,000		$ 1,905,005,000
Other assets	132,356,000		132,356,000		164,183,000
Total assets	1,987,243,000		1,987,243,000		2,069,188,000
Liabilities and partners' capital:
Mortgage notes payable and credit facility	1,225,047,000		1,225,047,000		1,251,067,000
Other liabilities	32,712,000		32,712,000		32,257,000
Partners' capital	729,484,000		729,484,000		785,864,000
Total liabilities and partners' capital	1,987,243,000		1,987,243,000		2,069,188,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	52,270,000	57,497,000	104,646,000	101,325,000
Operating and other expenses	(20,483,000)	(23,076,000)	(41,691,000)	(40,816,000)
Gain on sale of communities	5,682,000	11,216,000	5,682,000	65,267,000
Interest expense, net	(13,523,000)	(15,829,000)	(27,413,000)	(31,098,000)
Depreciation expense	(13,863,000)	(17,783,000)	(28,280,000)	(30,933,000)
Net income	10,083,000	12,025,000	12,944,000	63,745,000
Impairment of investment in unconsolidated entities	0	0	0	0
Expensed Acquisition, Development and Other Pursuit Costs and Impairment of Long-Lived Assets
Expensed costs related to acquisition, development and other pursuit costs and impairment of long-lived assets	2,017,000	195,000	2,732,000	440,000
Fund I and II
Combined summary of the operating results of the accounted for using the equity method
Costs in excess of equity in underlying net assets of the respective investments	4,929,000		4,929,000		5,439,000
Fund II
Combined summary of the operating results of the accounted for using the equity method
Maximum amount that will be paid for capital contributions made by partners (as a percent)			10.00%
Maximum amount that will be paid for capital contributions made by partners	8,910,000		8,910,000
Residual JV
Combined summary of the operating results of the accounted for using the equity method
Gain on sale of communities	$ 6,658,000		$ 7,548,000