Other Significant Transactions (Details Textual) (USD $)	9 Months Ended
	Sep. 30, 2014 Property	Sep. 30, 2013
Other Significant Transactions [Line Items]
Number of partnerships in legally sold portfolio	17
Number of consolidated apartment communities in legally sold portfolio	14
Number of unconsolidated apartment communities in legally sold portfolio	57
Non-recourse debt payable to a noncontrolling limited partner that was contributed to the partnership's capital	$ 9,200,000
Proceeds from Issuance of Preferred Stock and Preference Stock	123,620,000	0
Class A Cumulative Preferred Stock [Member]
Other Significant Transactions [Line Items]
Shares of Preferred Stock Issued	5,000,000
Dividend Rate of Preferred Stock Issued	6.875%
Par Value Per Share of Preferred Stock Issued	$ 0.01
Net Proceeds Per Share Of Preferred Stock Issued	$ 24.15
Gross Offering Price Per Share Of Preferred Stock Issued	$ 25.00
Deductions From Gross Offering Price Per Share Of Preferred Stock Issued	$ 0.85
Proceeds from Issuance of Preferred Stock and Preference Stock	120,800,000
Class Z Cumulative Preferred Stock [Member]
Other Significant Transactions [Line Items]
Shares of Preferred Stock Issued	117,400
Dividend Rate of Preferred Stock Issued	7.00%
Par Value Per Share of Preferred Stock Issued	$ 0.01
Net Proceeds Per Share Of Preferred Stock Issued	$ 25.14
Gross Offering Price Per Share Of Preferred Stock Issued	$ 25.65
Deductions From Gross Offering Price Per Share Of Preferred Stock Issued	$ 0.51
Proceeds from Issuance of Preferred Stock and Preference Stock	3,000,000
Acquired Apartment Community [Member]
Other Significant Transactions [Line Items]
Apartment Community Acquisition Price	118,500,000
Number of Apartment Homes in Apartment Communities	600
Preliminary purchase price allocation to in-place lease intangible assets	1,600,000
Fair Value of Acquisition Allocated to Real Estate	$ 116,900,000