Description of Business and Organization Description of Business and Organization Narrative (Details)	0 Months Ended	9 Months Ended
	Oct. 06, 2013 entity	Sep. 30, 2014 entity sqft
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Area of real estate property		10,000,000
OP units owned by the Company, percent		36.80%
Number of entities to be treated as taxable REIT subsidiary		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