Investments in Real Estate Entities (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2015 home community	Mar. 31, 2014	Dec. 31, 2014
Equity method investment
Impairment of Real Estate	$ 5,788,000	$ 0
Assets:
Real estate, net	1,524,554,000		1,617,627,000
Other assets	76,491,000		72,290,000
Total assets	1,601,045,000		1,689,917,000
Liabilities and partners' capital:
Mortgage notes payable and credit facility	968,524,000		980,128,000
Other liabilities	25,510,000		24,884,000
Partners' capital	607,011,000		684,905,000
Total liabilities and partners' capital	1,601,045,000		1,689,917,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	45,255,000	52,376,000
Operating and other expenses	(17,337,000)	(21,208,000)
Gain on sale of communities	32,490,000	0
Interest expense, net	(10,477,000)	(13,890,000)
Depreciation expense	(11,902,000)	(14,417,000)
Net income	38,029,000	2,861,000
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	1,187,000	715,000
Number of Real Estate Properties	254
Number of apartment homes included in operating apartment communities owned	74,178
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	3,347,000		3,880,000
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
Avalon Mills [Member]
Equity method investment
Impairment of Real Estate	800,000
Avalon at Edgewater [Member]
Equity method investment
Casualty Loss	21,844,000
Insurance Proceeds	22,000,000
Impairment of Real Estate	793,000
Expensed Acquisition, Development and Other Pursuit Costs and Impairment of Long-Lived Assets
Number of Real Estate Properties	2
Number of apartment homes included in operating apartment communities owned	168
Loss Contingency, New Claims Filed, Number	14
Loss Contingency, Number of Plaintiffs	100
New England [Member]
Equity method investment
Impairment of Real Estate	$ 4,195,000