Related Party Transactions (Details) (USD $)	12 Months Ended			0 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 23, 2011 Board Of Directors Chairman [Member]	Nov. 30, 1999 Board Of Directors Chairman [Member]	Dec. 31, 2011 Alexanders Inc [Member]	Dec. 31, 2011 Interstate Properties [Member]	Dec. 31, 2010 Interstate Properties [Member]	Dec. 31, 2009 Interstate Properties [Member]
Related Party Transactions With Affiliated Entity [Line Items]
Percentage of Company Owned by Related Party							6.30%
Percentage of Affiliated Entity Owned By Company						32.40%
Percentage Of Affiliated Entity Owned By Related Parties						27.20%
Fee And Other Income From Related Parties							$ 787,000	$ 815,000	$ 782,000
Related Party Transaction Annual Fee Percentage							4.00%
Related Party Transaction Description Of Transaction							We manage and lease the real estate assets of Interstate pursuant to a management agreement for which we receive an annual fee equal to 4% of annual base rent and percentage rent. The management agreement has a term of one year and is automatically renewable unless terminated by either of the parties on 60 days’ notice at the end of the term. We believe, based upon comparable fees charged by other real estate companies, that the management agreement terms are fair to us.
Related Party Transaction [Line Items]
Proceeds from the repayment of loan to officer	13,123,000	0	0	13,122,500
Loan to officer	13,123,000	0	0	13,122,500
Related Party Transaction, Date				Dec. 23, 2017
Related Party Transaction, Rate				1.27%
Related Party Transaction Maximum Borrowing Capacity					$ 15,000,000