Mortgage Notes Payable (Schedule of Mortgage Notes Payable) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Outstanding Loan Amount	$ 172,121		$ 172,242
Mortgages
Debt Instrument [Line Items]
Encumbered Properties	14
Outstanding Loan Amount	172,121		172,242
Effective Interest Rate	3.60%	[1]
Mortgages | Design Center
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	20,100		20,198
Effective Interest Rate	4.40%
Mortgages | Bleecker Street
Debt Instrument [Line Items]
Encumbered Properties	3
Outstanding Loan Amount	21,300		21,300
Effective Interest Rate	4.30%
Mortgages | Foot Locker
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	3,250		3,250
Effective Interest Rate	4.60%
Mortgages | Regal Parking Garage
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	3,000		3,000
Effective Interest Rate	4.50%
Mortgages | Duane Reade
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	8,400		8,400
Effective Interest Rate	3.60%
Mortgages | Washington Street Portfolio
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	4,718		4,741
Effective Interest Rate	4.40%
Mortgages | One Jackson Square
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	13,000		13,000
Effective Interest Rate	3.40%	[2]
Mortgages | 350 West 42nd Street
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	11,365		11,365
Effective Interest Rate	3.40%
Mortgages | 1100 Kings Highway
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	20,200		20,200
Effective Interest Rate	3.40%	[2]
Mortgages | 1623 Kings Highway
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	7,288		7,288
Effective Interest Rate	3.30%	[2]
Mortgages | 256 West 38th Street
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	24,500		24,500
Effective Interest Rate	3.10%	[2]
Mortgages | 229 West 36th Street
Debt Instrument [Line Items]
Encumbered Properties	1
Outstanding Loan Amount	$ 35,000		$ 35,000
Effective Interest Rate	2.90%	[2]

[1] Calculated on a weighted average basis for all mortgages outstanding as of March 31, 2015.

[2] Fixed through an interest rate swap agreement.