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Description of Business and Organization Narrative (Details) (USD $)
 0 Months Ended 3 Months Ended 9 Months Ended
Oct. 06, 2013
entity
Sep. 30, 2013
entity
Sep. 30, 2014
entity
sqft
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
OP units owned by the Company, percent     36.80%
Area of real estate property     10,000,000
Number of entities to be treated as TRS's     2
Number of entities acquired 4 4  
Office Building [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Area of real estate property     9,300,000
Number of properties     14
Office Building [Member] | Manhattan [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Area of real estate property     7,500,000
Number of properties     9
Office Building [Member] | Fairfield County, Connecticut and Westchester County, New York [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Area of real estate property     1,800,000
Number of properties     5
Development Parcel [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Number of properties     3
Retail Site [Member] | Manhattan and Westport, Connecticut [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Area of real estate property     204,175
Retail Site [Member] | Manhattan [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Area of real estate property     526,539
Number of properties     4
Retail Site [Member] | Westport, Connecticut [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Number of properties     2
Other Property [Member] | Stamford, Connecticut [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Area of real estate property     380,000
ESRT [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
OP units owned by the Company, percent     36.80%
Common Class A [Member] | ESRT [Member]
      
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]      
Par value     $ 0.01