Related Party Transactions - Excluded Properties and Businesses (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) office_and_property interest property	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Retail [Member] | Manhattan [Member]
Related Party Transaction [Line Items]
Number of properties (property) | office_and_property	4
Office Building [Member]
Related Party Transaction [Line Items]
Number of properties (property) | office_and_property	14
Office Building [Member] | Manhattan [Member]
Related Party Transaction [Line Items]
Number of properties (property) | office_and_property	9
Malkin Group [Member] | Mezzanine and Senior Equity Funds [Member]
Related Party Transaction [Line Items]
Number of interests owned (interest) | interest	2
Malkin Group [Member] | Residential Property Manager [Member]
Related Party Transaction [Line Items]
Number of properties (property) | interest	5
Number of interests owned (interest) | interest	5
Malkin Group [Member] | Multi-family Property [Member] | Greenwich, Connecticut [Member]
Related Party Transaction [Line Items]
Number of properties (property)	7
Malkin Group [Member] | Retail [Member] | Greenwich, Connecticut [Member]
Related Party Transaction [Line Items]
Number of properties (property)	5
Malkin Group [Member] | Retail [Member] | Manhattan [Member]
Related Party Transaction [Line Items]
Number of properties (property)	2
Malkin Group [Member] | Former Post Office [Member] | Greenwich, Connecticut [Member]
Related Party Transaction [Line Items]
Number of properties (property)	1
Malkin Group [Member] | Office Building [Member] | Manhattan [Member]
Related Party Transaction [Line Items]
Number of properties (property)	1
Supervisory fee revenue [Member] | Third party management and other fees [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Revenue from related parties | $	$ 1.1	$ 1.4	$ 1.8
Property management fee revenue [Member] | Third party management and other fees [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Revenue from related parties | $	$ 0.3	$ 0.4	$ 0.3