Investments in Partially Owned Entities (Related Party Transactions) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($)
Joint Venture \| Fifth Avenue and Times Square JV
Schedule of Equity Method Investments [Line Items]
Related party transaction annual fee percentage	2.00%
Supervisory fee, percentage	1.50%
Vornado Realty Trust \| Joint Venture \| Fifth Avenue and Times Square JV
Schedule of Equity Method Investments [Line Items]
Supervisory fee, percentage	5.00%
Fee and other income from related parties (in US dollars)	$ 3,085
Building Maintenance Service \| Majority-Owned Subsidiary, Unconsolidated
Schedule of Equity Method Investments [Line Items]
Revenue from related parties	$ 3,087

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=116637345&loc=SL114874292-224272

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration