Investments in Real Estate Entities (Details 2) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Assets:
Real estate, net	$ 1,624,119,000		$ 1,624,119,000		$ 1,905,005,000
Other assets	92,521,000		92,521,000		164,183,000
Total assets	1,716,640,000		1,716,640,000		2,069,188,000
Liabilities and partners' capital:
Mortgage notes payable and credit facility	982,246,000		982,246,000		1,251,067,000
Other liabilities	34,846,000		34,846,000		32,257,000
Partners' capital	699,548,000		699,548,000		785,864,000
Total liabilities and partners' capital	1,716,640,000		1,716,640,000		2,069,188,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	49,388,000	56,613,000	154,034,000	157,938,000
Operating and other expenses	(19,989,000)	(22,915,000)	(61,680,000)	(63,731,000)
Gain on sale of communities	327,539,000	5,395,000	333,221,000	70,662,000
Interest expense, net	(22,922,000)	(15,376,000)	(50,335,000)	(46,474,000)
Depreciation expense	(11,934,000)	(15,668,000)	(40,214,000)	(46,602,000)
Net income	322,082,000	8,049,000	335,026,000	71,793,000
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	407,000	351,000	3,138,000	792,000
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	4,108,000		4,108,000		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			$ 7,548,000