Investments in Real Estate Entities (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	$ 15,270	$ 70,744	$ 64,962
Gain on sale of communities	54,202	136,333	196,749
Fund I
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	0	0	87
Fund II
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	843	53,961	49,882
Equity in income of unconsolidated entities relating to the Company's recognition of promoted interest	925	26,472	7,985
Gain on sale of communities		26,322	41,501
US Fund
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	9,766	14,773	15,635
Gain on sale of communities	8,636	13,788
ACJV
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	3,527	1,388	1,445
Gain on sale of communities	2,019
MVPI LLC
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	1,917	1,833	1,627
Equity in income of unconsolidated entities relating to the Company's recognition of promoted interest			16,568
Brandywine
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	95	106	10
CVP I, LLC
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	0	0	9
Residual JV
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	(879)	(1,223)	(1,374)
Avalon Clarendon
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	0	0	(2,359)
AVA North Point
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	305	(122)	0
Sudbury
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	29	28	0
NYC JV
Summary of the Company's equity in income of unconsolidated entities
Equity in income of unconsolidated real estate entities	$ (333)	$ 0	$ 0