Commitments and Contingencies (Narrative) (Details) ft² in Thousands	1 Months Ended	3 Months Ended
	Nov. 30, 2011 extension	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2018 USD ($) ft²
Other Commitments
Lease liabilities		$ 497,531,000	$ 498,254,000
Right-of-use assets		378,257,000	$ 379,546,000
Guarantees and master leases		1,543,000,000
Clawback payment		24,300,000
Commitment to fund additional capital to partially owned entities		11,000,000
Construction commitment		559,000,000
General Liability
Insurance
Insurance limit per property		300,000,000
Insurance limit per occurrence		300,000,000
All Risk And Rental Value
Insurance
Insurance limit per occurrence		2,000,000,000.0
Earthquake California Properties
Insurance
Insurance limit per occurrence		350,000,000
Insurance maximum coverage limit in aggregate		$ 350,000,000
Vornado deductible, percentage of property value		5.00%
Non-Certified Acts of Terrorism
Insurance
Insurance maximum coverage limit in aggregate		$ 1,200,000,000
Terrorism Acts
Insurance
Insurance limit per occurrence		6,000,000,000
Insurance maximum coverage limit in aggregate		6,000,000,000.0
NBCR Acts
Insurance
Insurance limit per occurrence		5,000,000,000
Insurance maximum coverage limit in aggregate		5,000,000,000.0
PPIC | NBCR Acts
Insurance
Insurance deductible		$ 1,430,413
Insurance deductible percentage of balance of covered loss		20.00%
Farley Office and Retail Building | General Liability
Insurance
Insurance limit per occurrence		$ 100,000,000
Farley Office and Retail Building | Non-Certified Acts of Terrorism
Insurance
Insurance limit per occurrence		1,000,000,000.0
Insurance maximum coverage limit in aggregate		1,000,000,000.0
Farley Office and Retail Building | Terrorism Acts
Insurance
Insurance limit per occurrence		1,000,000,000.0
Insurance maximum coverage limit in aggregate		1,000,000,000.0
Farley Office and Retail Building | Property and Development Activities
Insurance
Insurance limit per occurrence		2,800,000,000
Insurance maximum coverage limit in aggregate		$ 2,800,000,000.0
Joint Venture | Farley Office and Retail Building
Other Commitments
Equity method ownership percentage		95.00%
345 Montgomery Street | Regus PLC
Other Commitments
Guarantor obligations, maximum exposure, undiscounted				$ 90,000,000
608 Fifth Avenue
Other Commitments
Lease liabilities		$ 71,071,000
Subsidiary of Regus PLC | 345 Montgomery Street
Other Commitments
Square footage of real estate property (in sqft) | ft²				78
Lessor, operating lease, lease not yet commenced, term of contract				15 years
New York City Economic Development Corporation
Other Commitments
Operating lease, term of contract	49 years
Leases, number of renewal terms | extension	5
Lease, term (in years)	10 years
Annual rent payments		2,000,000
Lease liabilities		45,790,000
Right-of-use assets		34,732,000
Unsecured Revolving Credit Facilities
Other Commitments
Outstanding letters of credit		$ 17,458,000