Organization	6 Months Ended
Jun. 30, 2016
Organization [Abstract]
Organization	1. Organization Alexander's, Inc. (NYSE: ALX) is a real estate investment trust (“REIT”), incorporated in Delaware, engaged in leasing, managing, developing and redeveloping its properties. All references to “we,” “us,” “our,” “Company” and “Alexander's” refer to Alexander's, Inc. and its consolidated subsidiaries. We are managed by, and our properties are leased and developed by, Vornado Realty Trust (“Vornado”) (NYSE: VNO).

The entire disclosure for the nature of an entity's business, major products or services, principal markets including location, and the relative importance of its operations in each business and the basis for the determination, including but not limited to, assets, revenues, or earnings. For an entity that has not commenced principal operations, disclosures about the risks and uncertainties related to the activities in which the entity is currently engaged and an understanding of what those activities are being directed toward.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=51801978&loc=d3e6003-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=51801978&loc=SL51803626-108592

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