Organization and Business (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2024 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	56
New York | Manhattan | Office Building
Real Estate Properties
Number of real estate properties | property	30
Square footage of real estate property (in sqft) | ft²	20.1
New York | Manhattan | Retail
Real Estate Properties
Number of real estate properties | property	49
Square footage of real estate property (in sqft) | ft²	2.4
New York | Manhattan | Residential Properties
Real Estate Properties
Number of real estate properties | property	2
Number of units in real estate property | unit	1,330
New York | New York City Metropolitan Area | Alexander's
Real Estate Properties
Number of real estate properties | property	5
Equity method ownership percentage	32.40%
New York | New York City Metropolitan Area | Alexander's | 731 Lexington Avenue
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 | unit	312
Other | Chicago | THE MART, Illinois
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	91.40%