Significant Transactions During the Third Quarter of 2013 and Subsequent Events (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended			1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended			1 Months Ended
	Aug. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Aug. 31, 2013 Structured Financing [Member]	Sep. 30, 2013 Structured Financing [Member]	Aug. 31, 2013 Secured Debt [Member]	Sep. 30, 2013 Secured Debt [Member]	Oct. 31, 2013 Secured Debt [Member] Subsequent Event [Member]	Sep. 30, 2013 Essex Apartment Value Fund II, LP [Member] Unit	Sep. 30, 2013 Slater 116 [Member] sqft Unit	Oct. 31, 2013 Vox Apartments [Member] Subsequent Event [Member] Unit	Aug. 31, 2013 Linden Square [Member]
Acquisitions [Abstract]
Cost of acquired entity													$ 29,600,000	$ 22,200,000
Number of units												4	108	58
Area of real estate property (in square feet)													10,200
Percentage of property leased (in hundredths)													44.00%
Percentage of property occupied (in hundredths)														100.00%
Dispositions [Abstract]
Sale of land held for future development												294,000,000			25,300,000
Ownership percentage in Fund II (in hundredths)												28.20%
Number of units disposed of												4	108	58
Penalty paid on repayment of debt												200,000
Gain on sale of land		0	0	1,503,000	0							137,800,000			12,700,000
Company's share of the gain on sale of assets												36,400,000
Secured Debt [Abstract]
Maturity period of debt instrument									7 years
Amount of construction loan replaced									45,000,000
Basis spread on rate (in hundredths)									1.50%
Description on variable interest rate									LIBOR
Amount of interest rate swap									45,000,000
Interest rate on interest rate swap (in hundredths)									3.70%
Repayment of debt				536,926,000	1,196,977,000					10,100,000	19,400,000
Undrawn capacity on unsecured debt										609,600,000
Structured Financing [Abstract]
Preferred equity investment in multifamily development project	8,500,000	674,075,000		674,075,000		571,345,000	8,500,000
Preferred return on preferred equity investment (in hundredths)	12.00%						12.00%
Investment period	3 years						3 years
Preferred equity investment, reduction rate, minimum (in hundredths)		9.00%						9.00%
Preferred equity investment, reduction rate, maximum (in hundredths)		13.00%						13.00%
Extended investment period		1 year						1 year
Income from preferred equity restructuring agreement		$ 40,802,000	$ 3,547,000	$ 52,295,000	$ 8,998,000			$ 400,000