Investments in Real Estate Entities (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Assets:
Real estate, net	$ 1,883,464,000		$ 1,890,496,000
Other assets	355,135,000		402,644,000
Total assets	2,238,599,000		2,293,140,000
Liabilities and partners' capital:
Mortgage notes payable and credit facility	1,249,276,000		1,251,067,000
Other liabilities	39,532,000		29,677,000
Partners' capital	949,791,000		1,012,396,000
Total liabilities and partners' capital	2,238,599,000		2,293,140,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	51,132,000	43,827,000
Operating and other expenses	(21,171,000)	(17,705,000)
Gain on sale of communities		54,051,000
Interest expense, net	(13,890,000)	(15,269,000)
Depreciation expense	(14,417,000)	(13,151,000)
Net income	1,654,000	51,753,000
Impairment of investment in unconsolidated entities	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	702,000	245,000
Fund I
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	7,500,000
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	8,910,000
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	$ 5,404,000		$ 5,439,000
Maximum amount that will be paid for capital contributions made by partners (as a percent)	10.00%