Investments in Partially Owned Entities (Summary of Income (Loss) ) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule Of Equity Method Investments
Our share of net income (loss)	$ 1,445	$ (4,240)
Alexanders Inc
Schedule Of Equity Method Investments
Equity method ownership percentage	32.40%
Equity in net income (loss)	$ 6,892	6,937
Management leasing and development fees	1,509	1,725
Our share of net income (loss)	$ 8,401	8,662
UE
Schedule Of Equity Method Investments
Equity method ownership percentage	5.40%
Equity in net income (loss)	$ 1,091	876
Management leasing and development fees	209	209
Our share of net income (loss)	1,300	1,085
Partially Owned Office Buildings
Schedule Of Equity Method Investments
Our share of net income (loss)	(10,054)	(14,249)
India real estate ventures
Schedule Of Equity Method Investments
Our share of net income (loss)	$ 1,654	(686)
India real estate ventures | Minimum
Schedule Of Equity Method Investments
Equity method ownership percentage	4.10%
India real estate ventures | Maximum
Schedule Of Equity Method Investments
Equity method ownership percentage	36.50%
PREIT
Schedule Of Equity Method Investments
Equity method ownership percentage	8.00%
Our share of net income (loss)	$ (2,830)	(4,288)
Other investments
Schedule Of Equity Method Investments
Our share of net income (loss)	$ 2,974	$ 5,236