Related Party Transactions - Excluded Properties and Businesses (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) office_and_property interest property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Retail | Manhattan
Related Party Transaction [Line Items]
Number of properties (property) | office_and_property	4
Office
Related Party Transaction [Line Items]
Number of properties (property) | office_and_property	14
Office | Manhattan
Related Party Transaction [Line Items]
Number of properties (property) | office_and_property	9
Malkin Group | Mezzanine and Senior Equity Funds
Related Party Transaction [Line Items]
Number of interests owned (interest) | interest	2
Malkin Group | Residential Property Manager
Related Party Transaction [Line Items]
Number of properties (property) | interest	5
Number of interests owned (interest) | interest	5
Malkin Group | Multi-family Property | Greenwich, Connecticut
Related Party Transaction [Line Items]
Number of properties (property)	8
Malkin Group | Retail | Greenwich, Connecticut
Related Party Transaction [Line Items]
Number of properties (property)	5
Malkin Group | Retail | Manhattan
Related Party Transaction [Line Items]
Number of properties (property)	2
Malkin Group | Former Post Office | Greenwich, Connecticut
Related Party Transaction [Line Items]
Number of properties (property)	1
Malkin Group | Office | Manhattan
Related Party Transaction [Line Items]
Number of properties (property)	1
Supervisory fee revenue | Third party management and other fees | Affiliated Entity
Related Party Transaction [Line Items]
Revenue from related parties | $	$ 1.1	$ 1.1	$ 1.4
Property management fee revenue | Third party management and other fees | Affiliated Entity
Related Party Transaction [Line Items]
Revenue from related parties | $	$ 0.3	$ 0.3	$ 0.4