Real Estate Disposition Activities (Details) ft² in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2020 USD ($) residential_condominium ft² home community	Jun. 30, 2020 USD ($) home	Mar. 31, 2020 USD ($) home	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) ft² residential_condominium community home	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Summary of income from discontinued operations
Gain on sale of communities	$ 31,607,000			$ 130,484,000	$ 91,338,000	$ 165,849,000
Number Of Communities Held For Sale | community	0				0
Number of Residential Condominium Units Sold | residential_condominium	7				59
Gain (Loss) on Sale of Other Investments					$ 8,174,000	0
Other Selling, General and Administrative Expense	$ 1,373,000			$ 1,108,000	4,012,000	$ 2,526,000
For-sale condominium inventory	$ 298,429,000				298,429,000		$ 457,809,000
Avalon Shelton [Member]
Summary of income from discontinued operations
Number Of Apartment Homes Sold | home			250
Proceeds from Sale of Real Estate			$ 64,750,000
Gain on sale of communities			$ 24,413,000
Avalon Tinton Falls [Member]
Summary of income from discontinued operations
Number Of Apartment Homes Sold | home		216
Proceeds from Sale of Real Estate		$ 64,900,000
Gain on sale of communities		$ 35,297,000
Avalon Towers [Member]
Summary of income from discontinued operations
Number Of Apartment Homes Sold | home	109
Proceeds from Sale of Real Estate	$ 54,000,000
Gain on sale of communities	31,603,000
The Park Loggia [Member]
Summary of income from discontinued operations
Proceeds from Sale of Real Estate	$ 15,699,000				$ 182,512,000
Number Of Residential Condominium Units | home	172				172
Commercial Square Feet | ft²	67				67
Gain (Loss) on Sale of Other Investments	$ 727,000				$ 8,174,000