Real Estate Disposition Activities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) community land_parcel home	Dec. 31, 2017 USD ($) home	Dec. 31, 2016 USD ($) home
Summary of income from discontinued operations
Gain on sale of communities	$ 374,976	$ 252,599	$ 374,623
Gain (loss) on other real estate transactions, net	$ 345	$ (10,907)	$ 10,224
Number of communities held for sale | community	1
Number of land parcels held for sale | land_parcel	2
Avalon Blue Hills/Avalon Canton at Blue Hills
Summary of income from discontinued operations
Apartment homes | home	472
Gross sales price	$ 131,250
Net cash proceeds	$ 129,466
Eaves North Quincy
Summary of income from discontinued operations
Apartment homes | home	224
Gross sales price	$ 64,250
Net cash proceeds	$ 63,302
Avalon Anaheim Stadium
Summary of income from discontinued operations
Apartment homes | home	251
Gross sales price	$ 111,600
Net cash proceeds	$ 105,495
Avalon Ballston Place
Summary of income from discontinued operations
Apartment homes | home	383
Gross sales price	$ 169,000
Net cash proceeds	$ 166,921
Avalon at Fairway Hills - Fields
Summary of income from discontinued operations
Apartment homes | home	192
Gross sales price	$ 39,500
Net cash proceeds	$ 38,744
Avalon Fashion Valley
Summary of income from discontinued operations
Apartment homes | home	161
Gross sales price	$ 70,750
Net cash proceeds	$ 69,781
Avalon Andover
Summary of income from discontinued operations
Apartment homes | home	115
Gross sales price	$ 32,400
Net cash proceeds	$ 31,765
NYC JV
Summary of income from discontinued operations
Apartment homes | home	1,301
Repayments of secured debt	$ 395,939
Other Real Estate Sales
Summary of income from discontinued operations
Gain (loss) on other real estate transactions, net	345
Gross sales price	639
Net cash proceeds	$ 1,040
Fairfax City Land
Summary of income from discontinued operations
Number of land parcels sold | land_parcel	1
Wholly Owned Properties Excluding NYC JV
Summary of income from discontinued operations
Number of apartment communities sold | community	8
Apartment homes | home	1,798
Sale of communities gross sales price	$ 618,750
Gain on sale of communities	$ 195,115
NYC JV
Summary of income from discontinued operations
Number of apartment communities sold | community	5
Sale of communities gross sales price	$ 758,900
Gain on sale of communities	179,861
Net cash proceeds	$ 276,799
Wholly Owned Properties
Summary of income from discontinued operations
Apartment homes | home	3,099	1,624	2,051
Repayments of secured debt	$ 395,939	$ 0	$ 0
Gross sales price	1,378,289	514,654	564,028
Net cash proceeds	$ 883,313	$ 503,039	$ 532,717
NYC JV
Summary of income from discontinued operations
Equity Method Investment, Ownership Percentage	20.00%