Mortgage Notes Payable, Net (Mortgage Note) (Details) $ in Thousands	Mar. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($)	Jul. 17, 2019 USD ($)
Debt Instrument [Line Items]
Mortgage notes payable, gross	$ 405,000
Mortgage notes payable, net	$ 395,417	$ 395,031
Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	7
Mortgage notes payable, gross	$ 405,000	405,000
Less: deferred financing costs, net	(9,583)	(9,969)
Mortgage notes payable, net	$ 395,417	395,031
Effective Interest Rate	4.35%
123 William Street
Debt Instrument [Line Items]
Escrow deposit	$ 2,500
123 William Street | Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	1
Mortgage notes payable, gross	$ 140,000	140,000
Effective Interest Rate	4.74%
1140 Avenue of the Americas | Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	1
Mortgage notes payable, gross	$ 99,000	99,000
Effective Interest Rate	4.18%
400 E. 67th Street - Laurel Condominium / 200 Riverside Boulevard - ICON Garage | Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	2
Mortgage notes payable, gross	$ 50,000	50,000
Effective Interest Rate	4.59%
8713 Fifth Avenue | Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	1
Mortgage notes payable, gross	$ 10,000	10,000
Effective Interest Rate	5.05%
9 Times Square | Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	1
Mortgage notes payable, gross	$ 55,000	55,000
Effective Interest Rate	3.73%
196 Orchard Street | Mortgages Note Payable
Debt Instrument [Line Items]
Encumbered Properties | property	1
Mortgage notes payable, gross	$ 51,000	$ 51,000	$ 51,000
Effective Interest Rate	3.91%		3.85%