Mortgage Notes Payable (Schedule of Mortgage Notes Payable) (Details) $ in Thousands		Jun. 30, 2015 USD ($) property	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Outstanding Loan Amount		$ 171,998	$ 172,242
Mortgages
Debt Instrument [Line Items]
Encumbered Properties | property		14
Outstanding Loan Amount		$ 171,998	172,242
Effective Interest Rate	[1]	3.60%
Mortgages | Design Center
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 20,000	20,198
Effective Interest Rate		4.40%
Mortgages | Bleecker Street
Debt Instrument [Line Items]
Encumbered Properties | property		3
Outstanding Loan Amount		$ 21,300	21,300
Effective Interest Rate		4.30%
Mortgages | Foot Locker
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 3,250	3,250
Effective Interest Rate		4.60%
Mortgages | Regal Parking Garage
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 3,000	3,000
Effective Interest Rate		4.50%
Mortgages | Duane Reade
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 8,400	8,400
Effective Interest Rate		3.60%
Mortgages | Washington Street Portfolio
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 4,695	4,741
Effective Interest Rate		4.40%
Mortgages | One Jackson Square
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 13,000	13,000
Effective Interest Rate	[2]	3.40%
Mortgages | 350 West 42nd Street
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 11,365	11,365
Effective Interest Rate		3.40%
Mortgages | 1100 Kings Highway
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 20,200	20,200
Effective Interest Rate	[2]	3.40%
Mortgages | 1623 Kings Highway
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 7,288	7,288
Effective Interest Rate	[2]	3.30%
Mortgages | 256 West 38th Street
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 24,500	24,500
Effective Interest Rate	[2]	3.10%
Mortgages | 229 West 36th Street
Debt Instrument [Line Items]
Encumbered Properties | property		1
Outstanding Loan Amount		$ 35,000	$ 35,000
Effective Interest Rate	[2]	2.90%

[1] Calculated on a weighted average basis for all mortgages outstanding as of June 30, 2015.

[2] Fixed through an interest rate swap agreement.