Organization (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2021 ft² segment unit property
Operating Properties
Number of properties | property	6
Number of segments | segment	1
Operating property | 731 Lexington Avenue
Operating Properties
Area of property (in square feet)	1,079
Operating property | 731 Lexington Avenue | Office space
Operating Properties
Area of property (in square feet)	939
Operating property | 731 Lexington Avenue | Retail space
Operating Properties
Area of property (in square feet)	140
Operating property | 731 Lexington Avenue | Retail space | Tenant Occupant | Home Depot
Operating Properties
Area of property (in square feet)	83
Operating property | Rego Park I | Anchor
Operating Properties
Area of property (in square feet)	338
Operating property | Rego Park I | Anchor | IKEA
Operating Properties
Area of property (in square feet)	112
Operating property | Rego Park I | Anchor | Burlington Coat Factory
Operating Properties
Area of property (in square feet)	50
Operating property | Rego Park I | Anchor | Bed Bath and Beyond
Operating Properties
Area of property (in square feet)	46
Operating property | Rego Park I | Anchor | Marshalls
Operating Properties
Area of property (in square feet)	36
Operating property | Rego Park II | Anchor
Operating Properties
Area of property (in square feet)	615
Operating property | Rego Park II | Anchor | Costco
Operating Properties
Area of property (in square feet)	145
Operating property | Rego Park II | Anchor | Kohl's
Operating Properties
Area of property (in square feet)	133
Operating property | The Alexander apartment tower
Operating Properties
Area of property (in square feet)	255
Number of property units | unit	312
Operating property | Flushing
Operating Properties
Area of property (in square feet)	167
Properties to be developed | Rego Park III
Operating Properties
Area of land	140