Disposals and Assets Held for Sale (Details Textual) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015 Property Units	Mar. 31, 2014 Property Units	Dec. 31, 2014 Property Units
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of consolidated apartment communities disposed	6	5	30
Number of apartment homes in consolidated apartment communities disposed	1,100	1,606	9,067
Net income (before gains on dispositions) generated by sold properties	$ 18,457,000	$ 12,040,000
Gain on dispositions of real estate, net of tax	85,693,000	69,492,000
Non-recourse property debt assumed in connection with real estate dispositions		29,800,000
Wholly And Partially Owned Consolidated Properties [Member] | Assets Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Apartment Communities	1
Number of apartment homes in apartment communities	84
Disposal Group Disposed Of By Sale Not Discontinued Operations [Member] | Wholly And Partially Owned Consolidated Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net income (before gains on dispositions) generated by sold properties		9,800,000
Debt prepayment penalties associated with apartment community sales included in gain on dispositions	$ 12,100,000	$ 5,800,000