Organization and Business (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2022 ft² unit property building
Alexander's
Real Estate Properties
Equity method ownership percentage	32.40%
New York | Manhattan
Real Estate Properties
Number of real estate properties | property	62
New York | Manhattan | Office Building
Real Estate Properties
Number of real estate properties | property	30
Square footage of real estate property (in sqft) | ft²	19.9
New York | Manhattan | Retail
Real Estate Properties
Number of real estate properties | property	56
Square footage of real estate property (in sqft) | ft²	2.6
New York | Manhattan | Residential Properties
Real Estate Properties
Number of real estate properties | property	6
Number of units in real estate property (in number of residential units) | unit	1,664
New York | New York City Metropolitan Area | Alexander's
Real Estate Properties
Number of real estate properties | property	6
Equity method ownership percentage	32.40%
New York | New York City Metropolitan Area | Alexander's | Lexington Avenue 731
Real Estate Properties
Square footage of real estate property (in sqft) | ft²	1.1
New York | New York City Metropolitan Area | Residential Properties | Alexander's
Real Estate Properties
Number of units in real estate property (in number of residential units) | unit	312
Other | Chicago | The Mart, Chicago
Real Estate Properties
Square footage of real estate property (in sqft) | ft²	3.7
Other | San Francisco | Office Building | 555 California Street, California
Real Estate Properties
Square footage of real estate property (in sqft) | ft²	1.8
Number of buildings | building	3
Other | San Francisco | Office Building | 555 California Street, California | 555 California Street, California
Real Estate Properties
Equity method ownership percentage	70.00%
Operating Partnership
Real Estate Properties
Common limited partnership interest in the Operating Partnership	92.00%