Description of Business and Organization - Narrative (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2020 ft² office_and_property parcel entity
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	10.1
Number of entities to be treated as taxable REIT subsidiary | entity	2
Office
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	9.4
Number of offices and properties | office_and_property	14
Office | Manhattan
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	7.6
Number of offices and properties | office_and_property	9
Office | Fairfield County, Connecticut and Westchester County, New York
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	1.8
Number of offices and properties | office_and_property	5
Development Parcel
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of offices and properties | parcel	3
Retail | Manhattan and Westport, Connecticut
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	0.2
Retail | Manhattan
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	0.5
Number of offices and properties | office_and_property	4
Retail | Westport, Connecticut
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of offices and properties | office_and_property	2
Other Property | Stamford, Connecticut
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property (in sqft)	0.4
Empire State Realty Trust | Empire State Realty OP
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
OP units owned by the Company, percent	60.10%