Real Estate Disposition Activities (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) community item	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) community land_parcel home item	Sep. 30, 2014 USD ($)	Dec. 31, 2008 USD ($)
Summary of income from discontinued operations
Number of Apartment Communities Sold | community			2
Number of Land Parcels Sold | land_parcel			2
Proceeds from Sale of Real Estate			$ 232,415	$ 186,651
Gain on sale of communities			146,745	229,200
Gain on sale of real estate	$ 0	$ 0	9,647	0
Impairment of Real Estate	$ 658	$ 0	$ (10,668)	$ 0
Number Of Communities Held For Sale | community	0		0
Avalon Lyndhurst [Member]
Summary of income from discontinued operations
Apartment homes | home			328
Proceeds from Sale of Real Estate			$ 99,000
Gain on sale of communities			35,216
Other Real Estate Sales [Member]
Summary of income from discontinued operations
Proceeds from Sale of Real Estate			23,820
Gain on sale of real estate			$ 9,626
Avalon on Stamford Harbor [Member]
Summary of income from discontinued operations
Apartment homes | home			323
Number of Boat Slips in Marina Communities | item	74		74
Proceeds from Sale of Real Estate			$ 115,500
Gain on sale of communities			70,936
Other Real Estate Sales [Member]
Summary of income from discontinued operations
Impairment of Real Estate					$ (5,933)
Avalon Mills [Member]
Summary of income from discontinued operations
Impairment of Real Estate			$ 800